Programs & Examples On #Undef

How to make a variable accessible outside a function?

Your variable declarations and their scope are correct. The problem you are facing is that the first AJAX request may take a little bit time to finish. Therefore, the second URL will be filled with the value of sID before the its content has been set. You have to remember that AJAX request are normally asynchronous, i.e. the code execution goes on while the data is being fetched in the background.

You have to nest the requests:

$.getJSON(""+input+"?api_key=API_KEY_HERE"  , function(name){   obj = name;   // sID is only now available!   sID =;   console.log(sID); }); 

Clean up your code!

  • Put the second request into a function
  • and let it accept sID as a parameter, so you don't have to declare it globally anymore! (Global variables are almost always evil!)
  • Remove sID and obj variables - is sufficient unless you really need the other variables outside the function.

$.getJSON(""+input+"?api_key=API_KEY_HERE"  , function(name){   // We don't need sID or obj here - is sufficient   console.log(;    doSecondRequest(; });  /// TODO Choose a better name function doSecondRequest(sID) {   $.getJSON("" + sID + "/summary?api_key=API_KEY_HERE", function(stats){         console.log(stats);   }); } 

Hapy New Year :)

Titlecase all entries into a form_for text field

You don't want to take care of normalizing your data in a view - what if the user changes the data that gets submitted? Instead you could take care of it in the model using the before_save (or the before_validation) callback. Here's an example of the relevant code for a model like yours:

class Place < ActiveRecord::Base   before_save do |place| = =   end end 

You can also check out the Ruby on Rails guide for more info.

To answer you question more directly, something like this would work:

<%= f.text_field :city, :value => ( ? : '') %>   

This just means if exists, display the titlecase version of it, and if it doesn't display a blank string.

Undefined Symbols error when integrating Apptentive iOS SDK via Cocoapods

We have found that adding the Apptentive cocoa pod to an existing Xcode project may potentially not include some of our required frameworks.

Check your linker flags:

Target > Build Settings > Other Linker Flags 

You should see -lApptentiveConnect listed as a linker flag:

... -ObjC -lApptentiveConnect ... 

You should also see our required Frameworks listed:

  • Accelerate
  • CoreData
  • CoreText
  • CoreGraphics
  • CoreTelephony
  • Foundation
  • QuartzCore
  • StoreKit
  • SystemConfiguration
  • UIKit

    -ObjC -lApptentiveConnect -framework Accelerate -framework CoreData -framework CoreGraphics -framework CoreText -framework Foundation -framework QuartzCore -framework SystemConfiguration -framework UIKit -framework CoreTelephony -framework StoreKit  

AngularJs directive not updating another directive's scope

Just wondering why you are using 2 directives?

It seems like, in this case it would be more straightforward to have a controller as the parent - handle adding the data from your service to its $scope, and pass the model you need from there into your warrantyDirective.

Or for that matter, you could use 0 directives to achieve the same result. (ie. move all functionality out of the separate directives and into a single controller).

It doesn't look like you're doing any explicit DOM transformation here, so in this case, perhaps using 2 directives is overcomplicating things.

Alternatively, have a look at the Angular documentation for directives: The very last example at the bottom of the page explains how to wire up dependent directives.

How to create a showdown.js markdown extension

In your last block you have a comma after 'lang', followed immediately with a function. This is not valid json.


It appears that the readme was incorrect. I had to to pass an array with the string 'twitter'.

var converter = new Showdown.converter({extensions: ['twitter']}); converter.makeHtml('whatever @meandave2020'); // output "<p>whatever <a href="">@meandave2020</a></p>" 

I submitted a pull request to update this.

TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received type undefined raised when starting react app

I just had this issue after installing and removing some npm packages and spent almost 5 hours to figure out what was going on.

What I did is basically copied my src/components in a different directory, then removed all the node modules and package-lock.json (if you are running your app in the Docker container, remove images and rebuild it just to be safe); then reset it to my last commit and then put back my src/components then ran npm i.

I hope it helps.

TS1086: An accessor cannot be declared in ambient context

I've updated typescript and tslint versions and removed packages I wasn't using. This solved the problem for me.

As others pointed here, it seems to be an issue with different TypeScript versions where the generated typings from some library aren't compatible with your TypeScript version.

Visual Studio Code PHP Intelephense Keep Showing Not Necessary Error

Here is I solved:

Open the extension settings:

enter image description here

And search for the variable you want to change, and unchecked/checked it

enter image description here

The variables you should consider are:


React Hook "useState" is called in function "app" which is neither a React function component or a custom React Hook function

Whenever working with a React functional component, always keep the first letter of the name of the component in Uppercase in order to avoid these React Hooks errors.

In your case, you have named the component app, which should be changed to App, as I said above, to avoid the React Hook error.

How can I solve the error 'TS2532: Object is possibly 'undefined'?

For others facing a similar problem to mine, where you know a particular object property cannot be null, you can use the non-null assertion operator (!) after the item in question. This was my code:

  const naciStatus = dataToSend.naci?.statusNACI;
  if (typeof naciStatus != "undefined") {
    switch (naciStatus) {
      case "AP":
        dataToSend.naci.certificateStatus = "FALSE";
      case "AS":
      case "WR":
        dataToSend.naci.certificateStatus = "TRUE";
        dataToSend.naci.certificateStatus = "";

And because dataToSend.naci cannot be undefined in the switch statement, the code can be updated to include exclamation marks as follows:

  const naciStatus = dataToSend.naci?.statusNACI;
  if (typeof naciStatus != "undefined") {
    switch (naciStatus) {
      case "AP":
        dataToSend.naci!.certificateStatus = "FALSE";
      case "AS":
      case "WR":
        dataToSend.naci!.certificateStatus = "TRUE";
        dataToSend.naci!.certificateStatus = "";

Typescript: Type 'string | undefined' is not assignable to type 'string'

Had the same issue.

I find out that react-scrips add "strict": true to tsconfig.json.

After I removed it everything works great.


Need to warn that changing this property means that you:

not being warned about potential run-time errors anymore.

as been pointed out by PaulG in comments! Thank you :)

Use "strict": false only if you fully understand what it affects!

Can't perform a React state update on an unmounted component

Edit: I just realized the warning is referencing a component called TextLayerInternal. That's likely where your bug is. The rest of this is still relevant, but it might not fix your problem.

1) Getting the instance of a component for this warning is tough. It looks like there is some discussion to improve this in React but there currently is no easy way to do it. The reason it hasn't been built yet, I suspect, is likely because components are expected to be written in such a way that setState after unmount isn't possible no matter what the state of the component is. The problem, as far as the React team is concerned, is always in the Component code and not the Component instance, which is why you get the Component Type name.

That answer might be unsatisfactory, but I think I can fix your problem.

2) Lodashes throttled function has a cancel method. Call cancel in componentWillUnmount and ditch the isComponentMounted. Canceling is more "idiomatically" React than introducing a new property.

TypeScript and React - children type?

A React Node is one of the following types:

  • Boolean (which is ignored)
  • null or undefined (which is ignored)
  • Number
  • String
  • A React element (result of JSX)
  • An array of any of the above, possibly a nested one

DeprecationWarning: Buffer() is deprecated due to security and usability issues when I move my script to another server

The use of the deprecated new Buffer() constructor (i.E. as used by Yarn) can cause deprecation warnings. Therefore one should NOT use the deprecated/unsafe Buffer constructor.

According to the deprecation warning new Buffer() should be replaced with one of:

  • Buffer.alloc()
  • Buffer.allocUnsafe() or
  • Buffer.from()

Another option in order to avoid this issue would be using the safe-buffer package instead.

You can also try (when using yarn..):

yarn global add yarn

as mentioned here: Link

Another suggestion from the comments (thx to gkiely): self-update

Note: self-update is not available. See policies for enforcing versions within a project

In order to update your version of Yarn, run

curl --compressed -o- -L | bash

Getting all documents from one collection in Firestore

Two years late but I just began reading the Firestore documentation recently cover to cover for fun and found withConverter which I saw wasn't posted in any of the above answers. Thus:

If you want to include ids and also use withConverter (Firestore's version of ORMs, like ActiveRecord for Ruby on Rails, Entity Framework for .NET, etc), then this might be useful for you:

Somewhere in your project, you probably have your Event model properly defined. For example, something like:

Your model (in TypeScript): ./models/Event.js

export class Event {
  constructor (
    public id: string,
    public title: string,
    public datetime: Date

export const eventConverter = {
  toFirestore: function (event: Event) {
    return {
      // id:,  // Note! Not in ".data()" of the model!
      title: event.title,
      datetime: event.datetime
  fromFirestore: function (snapshot: any, options: any) {
    const data =
    const id =
    return new Event(id, data.title, data.datetime)

And then your client-side TypeScript code:

import { eventConverter } from './models/Event.js'


async function loadEvents () {
  const qs = await firebase.firestore().collection('events')
    .orderBy('datetime').limit(3)  // Remember to limit return sizes!

  const events = any) =>


Two interesting quirks of Firestore to notice (or at least, I thought were interesting):

  1. Your is actually stored "one-level-up" in and not

  2. If you're using TypeScript, the TS linter (or whatever it's called) sadly isn't smart enough to understand:

const events = Event) =>

even though right above it you explicitly stated: .withConverter(eventConverter)

Which is why it needs to be doc: any.

(But! You will actually get Array<Event> back! (Not Array<Map> back.) That's the entire point of withConverter... That way if you have any object methods (not shown here in this example), you can immediately use them.)

It makes sense to me but I guess I've gotten so greedy/spoiled that I just kinda expect my VS Code, ESLint, and the TS Watcher to literally do everything for me. Oh well.

Formal docs (about withConverter and more) here:

Angular: How to download a file from HttpClient?

After spending much time searching for a response to this answer: how to download a simple image from my API restful server written in Node.js into an Angular component app, I finally found a beautiful answer in this web Angular HttpClient Blob. Essentially it consist on:

API Node.js restful:

   /* After routing the path you want ..*/
  public getImage( req: Request, res: Response) {

    // Check if file exist...
    if (!req.params.file) {
      return res.status(httpStatus.badRequest).json({
        ok: false,
        msg: 'File param not found.'
    const absfile = path.join(STORE_ROOT_DIR,IMAGES_DIR, req.params.file);

    if (!fs.existsSync(absfile)) {
      return res.status(httpStatus.badRequest).json({
        ok: false,
        msg: 'File name not found on server.'

Angular 6 tested component service (EmployeeService on my case):

  downloadPhoto( name: string) : Observable<Blob> {
    const url = environment.api_url + '/storer/employee/image/' + name;

    return this.http.get(url, { responseType: 'blob' })
        takeWhile( () => this.alive),
        filter ( image => !!image));


 <img [src]="" class="custom-photo" #photo>

Component subscriber and use:

@ViewChild('photo') image: ElementRef;

public LoadPhoto( name: string) {
          .subscribe( image => {
            const url= window.URL.createObjectURL(image);
            this.image.nativeElement.src= url;
          }, error => {
            console.log('error downloading: ', error);

Angular 6: saving data to local storage

First you should understand how localStorage works. you are doing wrong way to set/get values in local storage. Please read this for more information : How to Use Local Storage with JavaScript

Where to declare variable in react js

Assuming that onMove is an event handler, it is likely that its context is something other than the instance of MyContainer, i.e. this points to something different.

You can manually bind the context of the function during the construction of the instance via Function.bind:

class MyContainer extends Component {
  constructor(props) {

    this.onMove = this.onMove.bind(this);

    this.test = "this is a test";

  onMove() {

Also, test !== testVariable.

How to use ImageBackground to set background image for screen in react-native

Two options:

  1. Try setting width and height to width and height of the device screen
  2. Good old position absolute

Code for #2:

        <View style={{ flex: 1 }}>
           <Image style={{ width: screenWidth, height: screenHeight, position: 'absolute', top: 0, left: 0 }}/>
           <Text>Hey look, image background</Text>

Edit: For option #2 you can experiment with resizeMode="stretch|cover"

Edit 2: Keep in mind that option #2 renders the image and then everything after that in this order, which means that some pixels are rendered twice, this might have a very small performance impact (usually unnoticeable) but just for your information

How to read file with async/await properly?

You can easily wrap the readFile command with a promise like so:

async function readFile(path) {
    return new Promise((resolve, reject) => {
      fs.readFile(path, 'utf8', function (err, data) {
        if (err) {

then use:

await readFile("path/to/file");

React - clearing an input value after form submit

You are having a controlled component where input value is determined by So once you submit you have to clear your state which will clear your input automatically.

onHandleSubmit(e) {
    const city =;
      city: ''

ExpressionChangedAfterItHasBeenCheckedError: Expression has changed after it was checked. Previous value: 'undefined'

The ngAfterContentChecked lifecycle hook is triggered when bindings updates for the child components/directives have been already been finished. But you're updating the property that is used as a binding input for the ngClass directive. That is the problem. When Angular runs validation stage it detects that there's a pending update to the properties and throws the error.

To understand the error better, read these two articles:

Think about why you need to change the property in the ngAfterViewInit lifecycle hook. Any other lifecycle that is triggered before ngAfterViewInit/Checked will work, for example ngOnInit or ngDoCheck or ngAfterContentChecked.

So to fix it move renderWidgetInsideWidgetContainer to the ngOnInit() lifecycle hook.

Jest spyOn function called

You were almost done without any changes besides how you spyOn. When you use the spy, you have two options: spyOn the App.prototype, or component component.instance().

const spy = jest.spyOn(Class.prototype, "method")

The order of attaching the spy on the class prototype and rendering (shallow rendering) your instance is important.

const spy = jest.spyOn(App.prototype, "myClickFn");
const instance = shallow(<App />);

The App.prototype bit on the first line there are what you needed to make things work. A JavaScript class doesn't have any of its methods until you instantiate it with new MyClass(), or you dip into the MyClass.prototype. For your particular question, you just needed to spy on the App.prototype method myClickFn.

jest.spyOn(component.instance(), "method")

const component = shallow(<App />);
const spy = jest.spyOn(component.instance(), "myClickFn");

This method requires a shallow/render/mount instance of a React.Component to be available. Essentially spyOn is just looking for something to hijack and shove into a jest.fn(). It could be:

A plain object:

const obj = {a: x => (true)};
const spy = jest.spyOn(obj, "a");

A class:

class Foo {
    bar() {}

const nope = jest.spyOn(Foo, "bar");
// THROWS ERROR. Foo has no "bar" method.
// Only an instance of Foo has "bar".
const fooSpy = jest.spyOn(Foo.prototype, "bar");
// Any call to "bar" will trigger this spy; prototype or instance

const fooInstance = new Foo();
const fooInstanceSpy = jest.spyOn(fooInstance, "bar");
// Any call fooInstance makes to "bar" will trigger this spy.

Or a React.Component instance:

const component = shallow(<App />);
-> {myClickFn: f(), render: f(), ...etc}
const spy = jest.spyOn(component.instance(), "myClickFn");

Or a React.Component.prototype:

-> {myClickFn: f(), render: f(), ...etc}
const spy = jest.spyOn(App.prototype, "myClickFn");
// Any call to "myClickFn" from any instance of App will trigger this spy.

I've used and seen both methods. When I have a beforeEach() or beforeAll() block, I might go with the first approach. If I just need a quick spy, I'll use the second. Just mind the order of attaching the spy.

EDIT: If you want to check the side effects of your myClickFn you can just invoke it in a separate test.

const app = shallow(<App />);
Now assert your function does what it is supposed to do...

EDIT: Here is an example of using a functional component. Keep in mind that any methods scoped within your functional component are not available for spying. You would be spying on function props passed into your functional component and testing the invocation of those. This example explores the use of jest.fn() as opposed to jest.spyOn, both of which share the mock function API. While it does not answer the original question, it still provides insight on other techniques that could suit cases indirectly related to the question.

function Component({ myClickFn, items }) {
   const handleClick = (id) => {
       return () => myClickFn(id);
   return (<>
       {{id, name}) => (
           <div key={id} onClick={handleClick(id)}>{name}</div>

const props = { myClickFn: jest.fn(), items: [/*...{id, name}*/] };
const component = render(<Component {...props} />);
// Do stuff to fire a click event

Vue component event after render

updated() should be what you're looking for:

Called after a data change causes the virtual DOM to be re-rendered and patched.

The component’s DOM will have been updated when this hook is called, so you can perform DOM-dependent operations here.

React JS Error: is not defined react/jsx-no-undef

you should do import Map from './Map' React is just telling you it doesn't know where variable you are importing is.

Angular 2 ngfor first, last, index loop

Here is how its done in Angular 6

<li *ngFor="let user of userObservable ; first as isFirst">
   <span *ngIf="isFirst">default</span>

Note the change from let first = first to first as isFirst

'Property does not exist on type 'never'

In my case (I'm using typescript) I was trying to simulate response with fake data where the data is assigned later on. My first attempt was with:

let response = {status: 200, data: []};

and later, on the assignment of the fake data it starts complaining that it is not assignable to type 'never[]'. Then I defined the response like follows and it accepted it..

let dataArr: MyClass[] = [];
let response = {status: 200, data: dataArr};

and assigning of the fake data: = fakeData;

How to check undefined in Typescript

Adding this late answer to check for object.propertie that can help in some cases:

Using a juggling-check, you can test both null and undefined in one hit:

if ( == null) {

If you use a strict-check, it will only be true for values set to null and won't evaluate as true for undefined variables:

if ( === null) {

Typescript does NOT have a function to check if a variable is defined.

Update October 2020

You can now also use the nullish coallesing operator introduced in Typescript.

let neverNullOrUndefined = someValue ?? anotherValue;

Here, anotherValue will only be returned if someValue is null or undefined.

UndefinedMetricWarning: F-score is ill-defined and being set to 0.0 in labels with no predicted samples

As mentioned in the comments, some labels in y_test don't appear in y_pred. Specifically in this case, label '2' is never predicted:

>>> set(y_test) - set(y_pred)

This means that there is no F-score to calculate for this label, and thus the F-score for this case is considered to be 0.0. Since you requested an average of the score, you must take into account that a score of 0 was included in the calculation, and this is why scikit-learn is showing you that warning.

This brings me to you not seeing the error a second time. As I mentioned, this is a warning, which is treated differently from an error in python. The default behavior in most environments is to show a specific warning only once. This behavior can be changed:

import warnings
warnings.filterwarnings('always')  # "error", "ignore", "always", "default", "module" or "once"

If you set this before importing the other modules, you will see the warning every time you run the code.

There is no way to avoid seeing this warning the first time, aside for setting warnings.filterwarnings('ignore'). What you can do, is decide that you are not interested in the scores of labels that were not predicted, and then explicitly specify the labels you are interested in (which are labels that were predicted at least once):

>>> metrics.f1_score(y_test, y_pred, average='weighted', labels=np.unique(y_pred))

The warning is not shown in this case.

Class JavaLaunchHelper is implemented in two places

I am using Intellij Idea 2017 and I got into the same problem. What solved the problem for me was to simply

  1. close the project in intelliJ
  2. File -> New -> project from existing resources
  3. use Import from external model (if any)
  4. open the project again.

Make Axios send cookies in its requests automatically

I am not familiar with Axios, but as far as I know in javascript and ajax there is an option

withCredentials: true

This will automatically send the cookie to the client-side. As an example, this scenario is also generated with passportjs, which sets a cookie on the server

react router v^4.0.0 Uncaught TypeError: Cannot read property 'location' of undefined

I've tried everything suggested here but didn't work for me. So in case I can help anyone with a similar issue, every single tutorial I've checked is not updated to work with version 4.

Here is what I've done to make it work

import React from 'react';
import App from './App';

import ReactDOM from 'react-dom';
import {
} from 'react-router-dom';

                <Route path="/" render={()=><App items={temasArray}/>}/>
        </HashRouter >
    ), document.getElementById('root'));

That's the only way I have managed to make it work without any errors or warnings.

In case you want to pass props to your component for me the easiest way is this one:

 <Route path="/" render={()=><App items={temasArray}/>}/>

React.createElement: type is invalid -- expected a string

I had this problem when I added a css file to the same folder as the component file.

My import statement was:

import MyComponent from '../MyComponent'

which was fine when there was only a single file, MyComponent.jsx. (I saw this format in an example and gave it a try, then forgot I'd done it)

When I added MyComponent.scss to the same folder, the import then failed. Maybe JavaScript loaded the .scss file instead, and so there was no error.

My conclusion: always specify the file extension even if there is only one file, in case you add another one later.

Visual Studio 2017 errors on standard headers

I got the errors to go away by installing the Windows Universal CRT SDK component, which adds support for legacy Windows SDKs. You can install this using the Visual Studio Installer:

enter image description here

If the problem still persists, you should change the Target SDK in the Visual Studio Project : check whether the Windows SDK version is 10.0.15063.0.

In : Project -> Properties -> General -> Windows SDK Version -> select 10.0.15063.0.

Then errno.h and other standard files will be found and it will compile.

Cannot read property 'style' of undefined -- Uncaught Type Error

Add your <script> to the bottom of your <body>, or add an event listener for DOMContentLoaded following this StackOverflow question.

If that script executes in the <head> section of the code, document.getElementsByClassName(...) will return an empty array because the DOM is not loaded yet.

You're getting the Type Error because you're referencing search_span[0], but search_span[0] is undefined.

This works when you execute it in Dev Tools because the DOM is already loaded.

VueJs get url query

You can also get them with pure javascript.

For example:

new URL(location.href).searchParams.get('page')

For this url:, it would return a value of 1

Ansible: how to get output to display

Every Ansible task when run can save its results into a variable. To do this, you have to specify which variable to save the results into. Do this with the register parameter, independently of the module used.

Once you save the results to a variable you can use it later in any of the subsequent tasks. So for example if you want to get the standard output of a specific task you can write the following:

- hosts: localhost
    - shell: ls
      register: shell_result

    - debug:
        var: shell_result.stdout_lines

Here register tells ansible to save the response of the module into the shell_result variable, and then we use the debug module to print the variable out.

An example run would look like the this:

PLAY [localhost] ***************************************************************

TASK [command] *****************************************************************
changed: [localhost]

TASK [debug] *******************************************************************
ok: [localhost] => {
    "shell_result.stdout_lines": [

Responses can contain multiple fields. stdout_lines is one of the default fields you can expect from a module's response.

Not all fields are available from all modules, for example for a module which doesn't return anything to the standard out you wouldn't expect anything in the stdout or stdout_lines values, however the msg field might be filled in this case. Also there are some modules where you might find something in a non-standard variable, for these you can try to consult the module's documentation for these non-standard return values.

Alternatively you can increase the verbosity level of ansible-playbook. You can choose between different verbosity levels: -v, -vvv and -vvvv. For example when running the playbook with verbosity (-vvv) you get this:

PLAY [localhost] ***************************************************************

TASK [command] *****************************************************************
changed: [localhost] => {
    "changed": true,
    "cmd": "ls",
    "delta": "0:00:00.007621",
    "end": "2017-02-17 23:04:41.912570",
    "invocation": {
        "module_args": {
            "_raw_params": "ls",
            "_uses_shell": true,
            "chdir": null,
            "creates": null,
            "executable": null,
            "removes": null,
            "warn": true
        "module_name": "command"
    "rc": 0,
    "start": "2017-02-17 23:04:41.904949",
    "stderr": "",
    "stdout": "play.retry\nplay.yml",
    "stdout_lines": [
    "warnings": []

As you can see this will print out the response of each of the modules, and all of the fields available. You can see that the stdout_lines is available, and its contents are what we expect.

To answer your main question about the jenkins_script module, if you check its documentation, you can see that it returns the output in the output field, so you might want to try the following:

  - jenkins_script:
      script: (...)
    register: jenkins_result

  - debug:
      var: jenkins_result.output

How do I get rid of the b-prefix in a string in python?

you need to decode the bytes of you want a string:

b = b'1234'
print(b.decode('utf-8'))  # '1234'

How to disable button in React.js

I have had a similar problem, turns out we don't need hooks to do these, we can make an conditional render and it will still work fine.

        name === "" || email === "" || password === "" ? true : false

How to upgrade Angular CLI project?

To update Angular CLI to a new version, you must update both the global package and your project's local package.

Global package:

npm uninstall -g @angular/cli
npm cache clean
npm install -g @angular/cli@latest

Local project package:

rm -rf node_modules dist # use rmdir /S/Q node_modules dist in Windows Command Prompt; use rm -r -fo node_modules,dist in Windows PowerShell
npm install --save-dev @angular/cli@latest
npm install

See the reference

angular2: Error: TypeError: Cannot read property '...' of undefined

That's because abc is undefined at the moment of the template rendering. You can use safe navigation operator (?) to "protect" template until HTTP call is completed:


You can read more about safe navigation operator here.


Safe navigation operator can't be used in arrays, you will have to take advantage of NgIf directive to overcome this problem:

<div *ngIf="arr && arr.length > 0">

Read more about NgIf directive here.

Checking for Undefined In React

You can check undefined object using below code.

ReactObject === 'undefined'

Console logging for react?

If you're just after console logging here's what I'd do:

export default class App extends Component {
  componentDidMount() {
    console.log('I was triggered during componentDidMount')

  render() {
    console.log('I was triggered during render')
    return ( 
      <div> I am the App component </div>

Shouldn't be any need for those packages just to do console logging.

Using filesystem in node.js with async / await

This is the TypeScript version to the question. It is usable after Node 11.0:

import { promises as fs } from 'fs';

async function loadMonoCounter() {
    const data = await fs.readFile('monolitic.txt', 'binary');
    return Buffer.from(data);

Retrieve data from a ReadableStream object?

In order to access the data from a ReadableStream you need to call one of the conversion methods (docs available here).

As an example:

  .then(function(response) {
    // The response is a Response instance.
    // You parse the data into a useable format using `.json()`
    return response.json();
  }).then(function(data) {
    // `data` is the parsed version of the JSON returned from the above endpoint.
    console.log(data);  // { "userId": 1, "id": 1, "title": "...", "body": "..." }

EDIT: If your data return type is not JSON or you don't want JSON then use text()

As an example:

  .then(function(response) {
    return response.text();
  }).then(function(data) {
    console.log(data); // this will be a string

Hope this helps clear things up.

How to suppress "error TS2533: Object is possibly 'null' or 'undefined'"?

This is rather verbose and don't like it but it's the only thing that worked for me:

if (inputFile && inputFile.current) {
        ((inputFile.current as never) as HTMLInputElement).click()


if (inputFile && inputFile.current) { // also with ! or ? didn't work

didn't work for me. Typesript version: 3.9.7 with eslint and recommended rules.

Getting an object array from an Angular service

Take a look at your code :

 getUsers(): Observable<User[]> {
        return Observable.create(observer => {
            this.http.get('').map(response => response.json();

and code from (BTW. really good tutorial, you should check it out)

 getHeroes(): Promise<Hero[]> {
    return this.http.get(this.heroesUrl)
               .then(response => response.json().data as Hero[])

The HttpService inside Angular2 already returns an observable, sou don't need to wrap another Observable around like you did here:

   return Observable.create(observer => {
        this.http.get('').map(response => response.json()

Try to follow the guide in link that I provided. You should be just fine when you study it carefully.


First of all WHERE you log the this.users variable? JavaScript isn't working that way. Your variable is undefined and it's fine, becuase of the code execution order!

Try to do it like this:

  getUsers(): void {
            .then(users => {
               this.users = users
               console.log('this.users=' + this.users);


See where the console.log(...) is!

Try to resign from toPromise() it's seems to be just for ppl with no RxJs background.

Catch another link: Build your service once again with RxJs observables.

Safe navigation operator (?.) or (!.) and null property paths

Another alternative that uses an external library is _.has() from Lodash.


_.has(a, 'b.c')

is equal to

(a && a.b && a.b.c)

EDIT: As noted in the comments, you lose out on Typescript's type inference when using this method. E.g. Assuming that one's objects are properly typed, one would get a compilation error with (a && a.b && a.b.z) if z is not defined as a field of object b. But using _.has(a, 'b.z'), one would not get that error.

Deprecation warning in Moment.js - Not in a recognized ISO format

Check out all their awesome documentation!

Here is where they discuss the Warning Message.

String + Format

Warning: Browser support for parsing strings is inconsistent. Because there is no specification on which formats should be supported, what works in some browsers will not work in other browsers.

For consistent results parsing anything other than ISO 8601 strings, you should use String + Format.

moment("12-25-1995", "MM-DD-YYYY");

String + Formats (multiple formats)

If you have more than one format, check out their String + Formats (with an 's').

If you don't know the exact format of an input string, but know it could be one of many, you can use an array of formats.

moment("12-25-1995", ["MM-DD-YYYY", "YYYY-MM-DD"]);

Please checkout the documentation for anything more specific.


Checkout Parsing in Zone, the equivalent documentation for timezones.

The constructor takes all the same arguments as the moment constructor, but uses the last argument as a time zone identifier.

var b ="May 12th 2014 8PM", "MMM Do YYYY hA", "America/Toronto");


var dateFormat = "YYYY-M-D H:m"; //<-------- This part will get rid of the warning.
var aus1_s, aus2_s, aus3_s, aus4_s, aus5_s, aus6_s, aus6_e;
if ($("#custom1 :selected").val() == "AU" ) {
    var region = 'Australia/Sydney';

    aus1_s ='2016-9-26 19:30', dateFormat, region);              
    aus2_s ='2016-10-2 19:30', dateFormat, region);              
    aus3_s ='2016-10-9 19:30', dateFormat, region);                  
    aus4_s ='2016-10-16 19:30', dateFormat, region);                 
    aus5_s ='2016-10-23 19:30', dateFormat, region);
    aus6_s ='2016-10-30 19:30', dateFormat, region);
    aus6_e ='2016-11-5 19:30', dateFormat, region);
} else if ($("#custom1 :selected").val() == "NZ" ) {
    var region = 'Pacific/Auckland';

    aus1_s ='2016-9-28 20:30', dateFormat, region);
    aus2_s ='2016-10-4 20:30', dateFormat, region);
    aus3_s ='2016-10-11 20:30', dateFormat, region);
    aus4_s ='2016-10-18 20:30', dateFormat, region);
    aus5_s ='2016-10-25 20:30', dateFormat, region);
    aus6_s ='2016-11-2 20:30', dateFormat, region);
    aus6_e ='2016-11-9 20:30', dateFormat, region);

Read the current full URL with React?

To get the current router instance or current location you have to create a Higher order component with withRouter from react-router-dom. otherwise, when you are trying to access this.props.location it will return undefined


import React, { Component } from 'react';
import { withRouter } from 'react-router-dom';

class className extends Component {


export default withRouter(className)

Angular2: Cannot read property 'name' of undefined

This worked for me:

export class Hero{
   id: number;
   name: string;

   public Hero(i: number, n: string){ = 0; = '';

and make sure you initialize as well selectedHero

selectedHero: Hero = new Hero();

Pass react component as props

As noted in the accepted answer - you can use the special { props.children } property. However - you can just pass a component as a prop as the title requests. I think this is cleaner sometimes as you might want to pass several components and have them render in different places. Here's the react docs with an example of how to do it:

Make sure you are actually passing a component and not an object (this tripped me up initially).

The code is simply this:

const Parent = () => { 
  return (
    <Child  componentToPassDown={<SomeComp />}  />

const Child = ({ componentToPassDown }) => { 
  return (

Call to undefined function mysql_query() with Login

I would recommend that start using mysqli_() and stop using mysql_()

Check the following page: LINK

Warning This extension was deprecated in PHP 5.5.0, and it was removed in PHP 7.0.0. Instead, the MySQLi or PDO_MySQL extension should be used. See also MySQL: choosing an API guide and related FAQ for more information. Alternatives to this function include: mysqli_affected_rows() PDOStatement::rowCount()

Try and use mysqli_() Or PDO

DataTables: Cannot read property style of undefined


  • Number of th elements in the table header or footer differs from number of columns in the table body or defined using columns option.
  • Attribute colspan is used for th element in the table header.
  • Incorrect column index specified in columnDefs.targets option.


  • Make sure that number of th elements in the table header or footer matches number of columns defined in the columns option.
  • If you use colspan attribute in the table header, make sure you have at least two header rows and one unique th element for each column. See Complex header for more information.
  • If you use columnDefs.targets option, make sure that zero-based column index refers to existing columns.


See jQuery DataTables: Common JavaScript console errors - TypeError: Cannot read property ‘style’ of undefined for more information.

@ViewChild in *ngIf

In my case I needed to load a whole module only when the div existed in the template, meaning the outlet was inside an ngif. This way everytime angular detected the element #geolocalisationOutlet it created the component inside of it. The module only loads once as well.

    public wlService: WhitelabelService,
    public lmService: LeftMenuService,
    private loader: NgModuleFactoryLoader,
    private injector: Injector
) {

@ViewChild('geolocalisationOutlet', {read: ViewContainerRef}) set geolocalisation(geolocalisationOutlet: ViewContainerRef) {
    const path = 'src/app/components/engine/sections/geolocalisation/geolocalisation.module#GeolocalisationModule';
    this.loader.load(path).then((moduleFactory: NgModuleFactory<any>) => {
        const moduleRef = moduleFactory.create(this.injector);
        const compFactory = moduleRef.componentFactoryResolver
        if (geolocalisationOutlet && geolocalisationOutlet.length === 0) {

<div *ngIf="section === 'geolocalisation'" id="geolocalisation">
     <div #geolocalisationOutlet></div>

Error: Unexpected value 'undefined' imported by the module

In case your index exports a module - That module should not import its components from the same index, it should import them directly from the components file.

I had this issue, and when I changed from importing the components in the module file using the index to importing them using the direct file, this resolved.

e.g changed:

import { NgModule } from '@angular/core';
import { MainNavComponent } from './index';
  imports: [],
  exports: [MainNavComponent],
  declarations: [ MainNavComponent ],
  bootstrap:    [ MainNavComponent ]
export class MainNavModule {}


import { NgModule } from '@angular/core';
import { MainNavComponent } from './MainNavComponent';
  imports: [],
  exports: [MainNavComponent],
  declarations: [ MainNavComponent ],
  bootstrap:    [ MainNavComponent ]
export class MainNavModule {}

also remove the now unnecessary exports from you index, e.g:

export { MainNavModule } from './MainNavModule';
export { MainNavComponent } from './MainNavComponent';


export { MainNavModule } from './MainNavModule';

@viewChild not working - cannot read property nativeElement of undefined

The accepted answer is correct in all means and I stumbled upon this thread after I couldn't get the Google Map render in one of my app components.

Now, if you are on a recent angular version i.e. 7+ of angular then you will have to deal with the following ViewChild declaration i.e.

@ViewChild(selector: string | Function | Type<any>, opts: {
read?: any;
static: boolean;

Now, the interesting part is the static value, which by definition says

  • static - True to resolve query results before change detection runs

Now for rendering a map, I used the following ,

@ViewChild('map', { static: true }) mapElement: any;
  map: google.maps.Map;

Declare an array in TypeScript

Here are the different ways in which you can create an array of booleans in typescript:

let arr1: boolean[] = [];
let arr2: boolean[] = new Array();
let arr3: boolean[] = Array();

let arr4: Array<boolean> = [];
let arr5: Array<boolean> = new Array();
let arr6: Array<boolean> = Array();

let arr7 = [] as boolean[];
let arr8 = new Array() as Array<boolean>;
let arr9 = Array() as boolean[];

let arr10 = <boolean[]> [];
let arr11 = <Array<boolean>> new Array();
let arr12 = <boolean[]> Array();

let arr13 = new Array<boolean>();
let arr14 = Array<boolean>();

You can access them using the index:


and you add elements using push:


When creating the array you can supply the initial values:

let arr1: boolean[] = [true, false];
let arr2: boolean[] = new Array(true, false);

React Native: Possible unhandled promise rejection

Adding here my experience that hopefully might help somebody.

I was experiencing the same issue on Android emulator in Linux with hot reload. The code was correct as per accepted answer and the emulator could reach the internet (I needed a domain name).

Refreshing manually the app made it work. So maybe it has something to do with the hot reloading.

How to set component default props on React component

You can set the default props using the class name as shown below.

class Greeting extends React.Component {
  render() {
    return (
      <h1>Hello, {}</h1>

// Specifies the default values for props:
Greeting.defaultProps = {
  name: 'Stranger'

You can use the React's recommended way from this link for more info

Node.js heap out of memory

The following environment variable can be used:

NODE_OPTIONS= --max-old-space-size=8192 .

Another note: console.log() also consumes memory in the terminal.

just tried to comment the console.log() on terminal. because that will also take memory.

Import JavaScript file and call functions using webpack, ES6, ReactJS

import * as utils from './utils.js'; 

If you do the above, you will be able to use functions in utils.js as


Vue equivalent of setTimeout?

please use setInterval like below:


How to convert an object to JSON correctly in Angular 2 with TypeScript

If you are solely interested in outputting the JSON somewhere in your HTML, you could also use a pipe inside an interpolation. For example:

<p> {{ product | json }} </p>

I am not entirely sure it works for every AngularJS version, but it works perfectly in my Ionic App (which uses Angular 2+).

Moment.js - How to convert date string into date?

Sweet and Simple!

Dec 4, 2020 4:58 PM


moment.locale();         // en
moment().format('LT');   // 4:59 PM
moment().format('LTS');  // 4:59:47 PM
moment().format('L');    // 12/08/2020
moment().format('l');    // 12/8/2020
moment().format('LL');   // December 8, 2020
moment().format('ll');   // Dec 8, 2020
moment().format('LLL');  // December 8, 2020 4:59 PM
moment().format('lll');  // Dec 8, 2020 4:59 PM
moment().format('LLLL'); // Tuesday, December 8, 2020 4:59 PM
moment().format('llll'); // Tue, Dec 8, 2020 4:59 PM

Using an array from Observable Object with ngFor and Async Pipe Angular 2

Here's an example

// in the service
    return Observable.interval(2200).map(i=> [{name: 'car 1'},{name: 'car 2'}])

// in the controller
vehicles: Observable<Array<any>>
ngOnInit() {
    this.vehicles = this._vehicleService.getVehicles();

// in template
<div *ngFor='let vehicle of vehicles | async'>

Static image src in Vue.js template

This is how i solve it.:

      items: [
        { title: 'Dashboard', icon: require('@/assets/icons/sidebar/dashboard.svg') },
        { title: 'Projects',  icon: require('@/assets/icons/sidebar/projects.svg') },
        { title: 'Clients', icon: require('@/assets/icons/sidebar/clients.svg') },

And on the template part:

<img :src="item.icon" />

See it in action here

"Uncaught (in promise) undefined" error when using with=location in Facebook Graph API query

The reject actually takes one parameter: that's the exception that occurred in your code that caused the promise to be rejected. So, when you call reject() the exception value is undefined, hence the "undefined" part in the error that you get.

You do not show the code that uses the promise, but I reckon it is something like this:

var promise = doSth();
promise.then(function() { doSthHere(); });

Try adding an empty failure call, like this:

promise.then(function() { doSthHere(); }, function() {});

This will prevent the error to appear.

However, I would consider calling reject only in case of an actual error, and also... having empty exception handlers isn't the best programming practice.

Angular2 *ngIf check object array length in template

You can use

<div class="col-sm-12" *ngIf="event.attendees?.length">

Without event.attendees?.length > 0 or even event.attendees?length != 0

Because ?.length already return boolean value.

If in array will be something it will display it else not.

"SyntaxError: Unexpected token < in JSON at position 0"

In python you can use json.Dump(str) before send result to html template. with this command string convert to correct json format and send to html template. After send this result to JSON.parse(result) , this is correct response and you can use this.

Enzyme - How to access and set <input> value?

I am using create-react-app which comes with jest by default and enzyme 2.7.0.

This worked for me:

const wrapper = mount(<EditableText defaultValue="Hello" />);
const input = wrapper.find('input')[index]; // where index is the position of the input field of interest
input.node.value = 'Change';
input.simulate('change', input);

Angular 2: Passing Data to Routes?

You can't pass objects using router params, only strings because it needs to be reflected in the URL. It would be probably a better approach to use a shared service to pass data around between routed components anyway.

The old router allows to pass data but the new (RC.1) router doesn't yet.


data was re-introduced in RC.4 How do I pass data in Angular 2 components while using Routing?

Vue.JS: How to call function after page loaded?

You import the function from outside the main instance, and don't add it to the methods block. so the context of this is not the vm.

Either do this:

ready() {

or add the method to your methods first (which will make Vue bind this correctly for you) and call this method:

methods: {
  checkAuth: checkAuth
ready() {

How do I filter an array with TypeScript in Angular 2?

To filter an array irrespective of the property type (i.e. for all property types), we can create a custom filter pipe

import { Pipe, PipeTransform } from '@angular/core';

@Pipe({ name: "filter" })
export class ManualFilterPipe implements PipeTransform {
  transform(itemList: any, searchKeyword: string) {
    if (!itemList)
      return [];
    if (!searchKeyword)
      return itemList;
    let filteredList = [];
    if (itemList.length > 0) {
      searchKeyword = searchKeyword.toLowerCase();
      itemList.forEach(item => {
        //Object.values(item) => gives the list of all the property values of the 'item' object
        let propValueList = Object.values(item);
        for(let i=0;i<propValueList.length;i++)
          if (propValueList[i]) {
            if (propValueList[i].toString().toLowerCase().indexOf(searchKeyword) > -1)
    return filteredList;


//<tr *ngFor="let company of companyList | filter: searchKeyword"></tr>

Don't forget to import the pipe in the app module

We might need to customize the logic to filer with dates.

When should I use curly braces for ES6 import?

Usually when you export a function you need to use the {}.

If you have

export const x

you use

import {x} from ''

If you use

export default const x

you need to use

import x from ''

Here you can change X to whatever variable you want.

How to get the value of an input field using ReactJS?

You can get an input value without adding 'onChange' function.

Just add to the input element a 'ref attr:

And then use this.refs to get the input value when you need it.

Route.get() requires callback functions but got a "object Undefined"

check your closing tags in your model, it may be that you have defined a callback in another callback

How to fix Error: this class is not key value coding-compliant for the key tableView.'

Any chance that you changed the name of your table view from "tableView" to "myTableView" at some point?

check null,empty or undefined angularjs

just use -

if(!a) // if a is negative,undefined,null,empty value then...
    // do whatever
else {
    // do whatever

this works because of the == difference from === in javascript, which converts some values to "equal" values in other types to check for equality, as opposed for === which simply checks if the values equal. so basically the == operator know to convert the "", null, undefined to a false value. which is exactly what you need.

How to set default values for Angular 2 component properties?

Here is the best solution for this. (ANGULAR All Version)

Addressing solution: To set a default value for @Input variable. If no value passed to that input variable then It will take the default value.

I have provided solution for this kind of similar question. You can find the full solution from here

export class CarComponent implements OnInit {
  private _defaultCar: car = {
    // default isCar is true
    isCar: true,
    // default wheels  will be 4
    wheels: 4

  @Input() newCar: car = {};

  constructor() {}

  ngOnInit(): void {

   // this will concate both the objects and the object declared later (ie.. ...this.newCar )
   // will overwrite the default value. ONLY AND ONLY IF DEFAULT VALUE IS PRESENT

    this.newCar = { ...this._defaultCar, ...this.newCar };
   //  console.log(this.newCar);

Angular2 get clicked element id

do like this simply: (as said in comment here is with example with two methods)

import {Component} from 'angular2/core';

    selector: 'my-app', 
    template: `
      <button (click)="checkEvent($event,'a')" id="abc" class="def">Display Toastr</button>
      <button (click)="checkEvent($event,'b')" id="abc1" class="def1">Display Toastr1</button>
export class AppComponent {
  checkEvent(event, id){
    console.log(event, id,;


How to use a typescript enum value in an Angular2 ngSwitch statement

You can create a reference to the enum in your component class (I just changed the initial character to be lower-case) and then use that reference from the template (plunker):

import {Component} from 'angular2/core';

enum CellType {Text, Placeholder}
class Cell {
  constructor(public text: string, public type: CellType) {}
  selector: 'my-app',
  template: `
    <div [ngSwitch]="cell.type">
      <div *ngSwitchCase="cellType.Text">
      <div *ngSwitchCase="cellType.Placeholder">
    <button (click)="setType(cellType.Text)">Text</button>
    <button (click)="setType(cellType.Placeholder)">Placeholder</button>
export default class AppComponent {

  // Store a reference to the enum
  cellType = CellType;
  public cell: Cell;

  constructor() {
    this.cell = new Cell("Hello", CellType.Text)

  setType(type: CellType) {
    this.cell.type = type;

Send multipart/form-data files with angular using $http

In angular 9, Before tried 'Content-Type': undefined, but it is not worked for me then I tried the below code and It works like charms for a file object

const request =, data, {
      headers: {
        'Content-Type': 'file'

python-How to set global variables in Flask?


global index_add_counter

You are not defining, just declaring so it's like saying there is a global index_add_counter variable elsewhere, and not create a global called index_add_counter. As you name don't exists, Python is telling you it can not import that name. So you need to simply remove the global keyword and initialize your variable:

index_add_counter = 0

Now you can import it with:

from app import index_add_counter

The construction:

global index_add_counter

is used inside modules' definitions to force the interpreter to look for that name in the modules' scope, not in the definition one:

index_add_counter = 0
def test():
  global index_add_counter # means: in this scope, use the global name

React with ES7: Uncaught TypeError: Cannot read property 'state' of undefined

You have to bind your event handlers to correct context (this):


Angular: conditional class with *ngClass

That's the normal structure for ngClass is:

[ngClass]="{'classname' : condition}"

So in your case, just use it like this...

<ol class="breadcrumb">
  <li [ngClass]="{'active': step==='step1'}" (click)="step='step1'">Step1</li>
  <li [ngClass]="{'active': step==='step2'}" (click)="step='step2'">Step2</li>
  <li [ngClass]="{'active': step==='step3'}" (click)="step='step3'">Step3</li>

How to create an Observable from static data similar to http one in Angular?

Perhaps you could try to use the of method of the Observable class:

import { Observable } from 'rxjs/Observable';
import 'rxjs/add/observable/of';

public fetchModel(uuid: string = undefined): Observable<string> {
  if(!uuid) {
    return Observable.of(new TestModel()).map(o => JSON.stringify(o));
  else {
    return this.http.get("http://localhost:8080/myapp/api/model/" + uuid)
            .map(res => res.text());

How to access global variables

I would "inject" the starttime variable instead, otherwise you have a circular dependency between the packages.


var StartTime = time.Now()
func main() {
   otherPackage.StartTime = StartTime


var StartTime time.Time

Angular 2 @ViewChild annotation returns undefined

For me the problem was I was referencing the ID on the element.

@ViewChild('survey-form') slides:IonSlides;

<div id="survey-form"></div>

Instead of like this:

@ViewChild('surveyForm') slides:IonSlides;

<div #surveyForm></div>

Fatal error: Uncaught Error: Call to undefined function mysql_connect()

For mysqli you can use :

$db = ADONewConnection('mysqli');

... ...

$db->execute("set names 'utf8'");

setState(...): Can only update a mounted or mounting component. This usually means you called setState() on an unmounted component. This is a no-op

I encountered this issue because I used setState instead of state in the constructor.


Change the following incorrect code

constructor(props) {
    key: ''


constructor(props) {
  this.state = {
    key: ''

setTimeout in React Native

Change this code:

setTimeout(function(){this.setState({timePassed: true})}, 1000);

to the following:

setTimeout(()=>{this.setState({timePassed: true})}, 1000); 

JavaScript: Difference between .forEach() and .map()

Diffrence between Foreach & map :

Map() : If you use map then map can return new array by iterating main array.

Foreach() : If you use Foreach then it can not return anything for each can iterating main array.

useFul link : use this link for understanding diffrence

DataTables: Cannot read property 'length' of undefined

While the above answers describe the situation well, while troubleshooting the issue check also that browser really gets the format DataTables expects. There maybe other reasons not to get the data. For example, if the user does not have access to the data URL and gets some HTML instead. Or the remote system has some unfortunate "fix-ups" in place. Network tab in the browser's Debug tools helps.

Return from a promise then()

I prefer to use "await" command and async functions to get rid of confusions of promises,

In this case I would write an asynchronous function first, this will be used instead of the anonymous function called under "promise.then" part of this question :

async function SubFunction(output){

   // Call to database , returns a promise, like an Ajax call etc :

   const response = await axios.get( GetApiHost() + '/api/some_endpoint')

   // Return :
   return response;


and then I would call this function from main function :

async function justTesting() {
   const lv_result = await SubFunction(output);

   return lv_result + 1;

Noting that I returned both main function and sub function to async functions here.

"Call to undefined function mysql_connect()" after upgrade to php-7

From the PHP Manual:

Warning This extension was deprecated in PHP 5.5.0, and it was removed in PHP 7.0.0. Instead, the MySQLi or PDO_MySQL extension should be used. See also MySQL: choosing an API guide. Alternatives to this function include:



use MySQLi or PDO

$con = mysqli_connect('localhost', 'username', 'password', 'database');

React: "this" is undefined inside a component function

You can rewrite how your onToggleLoop method is called from your render() method.

render() {
    var shuffleClassName = this.state.toggleActive ? "player-control-icon active" : "player-control-icon"

return (
  <div className="player-controls">
      onClick={(event) => this.onToggleLoop(event)}

The React documentation shows this pattern in making calls to functions from expressions in attributes.

How to import and export components using React + ES6 + webpack?

To export a single component in ES6, you can use export default as follows:

class MyClass extends Component {

export default MyClass;

And now you use the following syntax to import that module:

import MyClass from './MyClass.react'

If you are looking to export multiple components from a single file the declaration would look something like this:

export class MyClass1 extends Component {

export class MyClass2 extends Component {

And now you can use the following syntax to import those files:

import {MyClass1, MyClass2} from './MyClass.react'

Warning: Failed propType: Invalid prop `component` supplied to `Route`

Standardize your module's imports and exports then you won't risk hitting problems with misspelled property names.

module.exports = Component should become export default Component.

CommonJS uses module.exports as a convention, however, this means that you are just working with a regular Javascript object and you are able to set the value of any key you want (whether that's exports, exoprts or exprots). There are no runtime or compile-time checks to tell you that you've messed up.

If you use ES6 (ES2015) syntax instead, then you are working with syntax and keywords. If you accidentally type exoprt default Component then it will give you a compile error to let you know.

In your case, you can simplify the Speaker component.

import React from 'react';

export default React.createClass({
  render() {
    return (

Checking for multiple conditions using "when" on single task in ansible

You can use like this.

when: condition1 == "condition1" or condition2 == "condition2"

Link to official docs: The When Statement.

Also Please refer to this gist:

Converting std::__cxx11::string to std::string

Is it possible that you are using GCC 5?

If you get linker errors about undefined references to symbols that involve types in the std::__cxx11 namespace or the tag [abi:cxx11] then it probably indicates that you are trying to link together object files that were compiled with different values for the _GLIBCXX_USE_CXX11_ABI macro. This commonly happens when linking to a third-party library that was compiled with an older version of GCC. If the third-party library cannot be rebuilt with the new ABI then you will need to recompile your code with the old ABI.

Source: GCC 5 Release Notes/Dual ABI

Defining the following macro before including any standard library headers should fix your problem: #define _GLIBCXX_USE_CXX11_ABI 0

How to execute raw queries with Laravel 5.1?

    DB::statement("your query")

I used it for add index to column in migration

react native get TextInput value

Every thing is OK for me by this procedure:

<Input onChangeText={this.inputOnChangeText} />

and also:

inputOnChangeText = (e) => {
    username: e

Call to undefined function App\Http\Controllers\ [ function name ]

If they are in the same controller class, it would be:

foreach ( $characters as $character) {
    $num += $this->getFactorial($index) * $index;
    $index ++;

Otherwise you need to create a new instance of the class, and call the method, ie:

$controller = new MyController();
foreach ( $characters as $character) {
    $num += $controller->getFactorial($index) * $index;
    $index ++;

javascript Unable to get property 'value' of undefined or null reference

You can't access element like you did (document.frm_new_user_request). You have to use the function getElementById:


So getting a value from an input could look like this:

var value = document.getElementById("frm_new_user_request").value

Also you can use some JavaScript framework, e.g. jQuery, which simplifies operations with DOM (Document Object Model) and also hides differences between various browsers from you.

Getting a value from an input using jQuery would look like this:

  • input with ID "element": var value = $("#element).value
  • input with class "element": var value = $(".element).value

How to properly export an ES6 class in Node 4?

Several of the other answers come close, but honestly, I think you're better off going with the cleanest, simplest syntax. The OP requested a means of exporting a class in ES6 / ES2015. I don't think you can get much cleaner than this:

'use strict';

export default class ClassName {
  constructor () {

Check if value exists in the array (AngularJS)

You could use indexOf function.

if(list.indexOf(createItem.artNr) !== -1) {
  $scope.message = 'artNr already exists!';

More about indexOf:

How to pass props to {this.props.children}

Cleaner way considering one or more children

   {, child => React.cloneElement(child, {...this.props}))}

React - uncaught TypeError: Cannot read property 'setState' of undefined

Arrow function could have make your life more easier to avoid binding this keyword. Like so:

 delta = () => {
           count : this.state.count++

Response::json() - Laravel 5.1

use the helper function in laravel 5.1 instead:

return response()->json(['name' => 'Abigail', 'state' => 'CA']);

This will create an instance of \Illuminate\Routing\ResponseFactory. See the phpDocs for possible parameters below:

* Return a new JSON response from the application.
* @param string|array $data
* @param int $status
* @param array $headers
* @param int $options
* @return \Symfony\Component\HttpFoundation\Response 
* @static 
public static function json($data = array(), $status = 200, $headers = array(), $options = 0){

    return \Illuminate\Routing\ResponseFactory::json($data, $status, $headers, $options);

Why es6 react component works only with "export default"?

Add { } while importing and exporting: export { ... }; | import { ... } from './Template';

exportimport { ... } from './Template'

export defaultimport ... from './Template'

Here is a working example:

// ExportExample.js
import React from "react";

function DefaultExport() {
  return "This is the default export";

function Export1() {
  return "Export without default 1";

function Export2() {
  return "Export without default 2";

export default DefaultExport;
export { Export1, Export2 };

// App.js
import React from "react";
import DefaultExport, { Export1, Export2 } from "./ExportExample";

export default function App() {
  return (
        <DefaultExport />
      <br />
      <Export1 />
      <br />
      <Export2 />

??Working sandbox to play around:

Ansible date variable

The filter option filters only the first level subkey below ansible_facts

PHP: Call to undefined function: simplexml_load_string()

To fix this error on Centos 7:

  1. Install PHP extension:

    sudo yum install php-xml

  2. Restart your web server. In my case it's php-fpm:

    services php-fpm restart

How to use lodash to find and return an object from Array?

You can use the following

import { find } from 'lodash'

Then to return the entire object (not only its key or value) from the list with the following:

let match = find(savedViews, { 'ID': 'id to match'});

Fatal error: Call to a member function query() on null

put this line in parent construct : $this->load->database();

function  __construct() {

this way.. it should work..

React fetch data in server before render

I've just stumbled upon this problem too, learning React, and solved it by showing spinner until the data is ready.

    render() {
    if ( === null) {
        return (
            <div className="MyView">
    else {
            <div className="MyView">
                <ReactJson src={}/>

Parse XLSX with Node and create json

I found a better way of doing this

  function genrateJSONEngine() {
    var XLSX = require('xlsx');
    var workbook = XLSX.readFile('test.xlsx');
    var sheet_name_list = workbook.SheetNames;
    sheet_name_list.forEach(function (y) {
      var array = workbook.Sheets[y];

      var first = array[0].join()
      var headers = first.split(',');

      var jsonData = [];
      for (var i = 1, length = array.length; i < length; i++) {

        var myRow = array[i].join();
        var row = myRow.split(',');

        var data = {};
        for (var x = 0; x < row.length; x++) {
          data[headers[x]] = row[x];


Call an overridden method from super class in typescript

below is an generic example

    //base class
    class A {
        // The virtual method
        protected virtualStuff1?():void;
        public Stuff2(){
            //Calling overridden child method by parent if implemented
            this.virtualStuff1 && this.virtualStuff1();
            alert("Baseclass Stuff2");
    //class B implementing virtual method
    class B extends A{
        // overriding virtual method
        public virtualStuff1()
            alert("Class B virtualStuff1");
    //Class C not implementing virtual method
    class C extends A{
    var b1 = new B();
    var c1= new C();

How to remove undefined and null values from an object using lodash?

With lodash (or underscore) You may do

var my_object = { a:undefined, b:2, c:4, d:undefined, e:null };

var passedKeys = _.reject(Object.keys(my_object), function(key){ return _.isUndefined(my_object[key]) || _.isNull(my_object[key]) })

newObject = {};
_.each(passedKeys, function(key){
    newObject[key] = my_object[key];

Otherwise, with vanilla JavaScript, you can do

var my_object = { a:undefined, b:2, c:4, d:undefined };
var new_object = {};

    if (typeof my_object[key] != 'undefined' && my_object[key]!=null){
        new_object[key] = my_object[key];

Not to use a falsey test, because not only "undefined" or "null" will be rejected, also is other falsey value like "false", "0", empty string, {}. Thus, just to make it simple and understandable, I opted to use explicit comparison as coded above. is not a function

The SIMPLEST answer is to put "data" into a pair of square brackets (i.e. [data]):

     $.getJSON("json/products.json").done(function (data) {

         var allProducts = [data].map(function (item) {
             return new getData(item);


Here, [data] is an array, and the ".map" method can be used on it. It works for me! enter image description here

how to use php DateTime() function in Laravel 5

DateTime is not a function, but the class.

When you just reference a class like new DateTime() PHP searches for the class in your current namespace. However the DateTime class obviously doesn't exists in your controllers namespace but rather in root namespace.

You can either reference it in the root namespace by prepending a backslash:

$now = new \DateTime();

Or add an import statement at the top:

use DateTime;

$now = new DateTime();

checking for typeof error in JS

Or use this for different types of errors

function isError(val) {
  return (!!val && typeof val === 'object')
    && (( === '[object Error]')
      || (typeof val.message === 'string' && typeof === 'string'))

How can I set the initial value of Select2 when using AJAX? only this solved my problem. even you set default value by option, you have to format the object, which has the text attribute and this is what you want to show in your option. so, your format function have to use || to choose the attribute which is not empty.

Passing data from controller to view in Laravel

public function showstudents() {
     $students = DB::table('student')->get();
     return (View::make("user/regprofile", compact('student')));

PHP - check if variable is undefined

You can use -

Ternary oprator to check wheather value set by POST/GET or not somthing like this

$value1 = $_POST['value1'] = isset($_POST['value1']) ? $_POST['value1'] : '';
$value2 = $_POST['value2'] = isset($_POST['value2']) ? $_POST['value2'] : '';
$value3 = $_POST['value3'] = isset($_POST['value3']) ? $_POST['value3'] : '';
$value4 = $_POST['value4'] = isset($_POST['value4']) ? $_POST['value4'] : '';

React JS - Uncaught TypeError: is not a function

More generally, you can also convert the new data into an array and use something like concat:

var newData =[data]);  
this.setState({data: newData})

This pattern is actually used in Facebook's ToDo demo app (see the section "An Application") at

How to run a task when variable is undefined in ansible?

As per latest Ansible Version 2.5, to check if a variable is defined and depending upon this if you want to run any task, use undefined keyword.

    - shell: echo "I've got '{{ foo }}' and am not afraid to use it!"
      when: foo is defined

    - fail: msg="Bailing out. this play requires 'bar'"
      when: bar is undefined

Ansible Documentation

reactjs giving error Uncaught TypeError: Super expression must either be null or a function, not undefined

For those using react-native:

import React, {
} from 'react-native';

may produce this error.

Whereas referencing react directly is the more stable way to go:

import React, { Component } from 'react';
import { StyleSheet } from 'react-native';

How to resolve TypeError: Cannot convert undefined or null to object

Make sure that destination object is not empty ( null or undefined ).

You can initialize destination object with empty object like below:

var destinationObj = {};

Object.assign(destinationObj, sourceObj);

String field value length in mongoDB

I had a similar kind of scenario, but in my case string is not a 1st level attribute. It is inside an object. In here I couldn't find a suitable answer for it. So I thought to share my solution with you all(Hope this will help anyone with a similar kind of problem).

Parent Collection 

"name":"Random Name",

Ex: If we need to get only collections that having child's name's length is higher than 10 characters.

 db.getCollection('Parent').find({$where: function() { 
for (var field in { 
    if ( > 10) 
        return true;


Javascript Uncaught TypeError: Cannot read property '0' of undefined

The error is here:


You are passing the first item of words, instead of the array.

Instead, pass the array to the function:


Problem solved!

Here's a breakdown of what the problem was:

I'm guessing in your browser (chrome throws a different error), words[] == words[0], so when you call hasLetter("a",words[]);, you are actually calling hasLetter("a",words[0]);. So, in essence, you are passing the first item of words to your function, not the array as a whole.

Of course, because words is just an empty array, words[0] is undefined. Therefore, your function call is actually:

hasLetter("a", undefined);

which means that, when you try to access d[ascii], you are actually trying to access undefined[0], hence the error.

Where is android_sdk_root? and how do I set it.?

android_sdk_root is a system variable which points to root folder of android sdk tools. You probably get the error because the variable is not set. To set it in Android Studio go to:

  1. File -> project Structure into Project Structure
  2. Left -> SDK Location
  3. SDK location select Android SDK location

If you have installed android SDK please refer to this answer to find the path to it:

Getting Cannot read property 'offsetWidth' of undefined with bootstrap carousel script

For me, I changed class='carousel-item' to class='item' like this

<div class="item">
    <img class="img-responsive" src="..." alt="...">

Is there a way to check for both `null` and `undefined`?

Using a juggling-check, you can test both null and undefined in one hit:

if (x == null) {

If you use a strict-check, it will only be true for values set to null and won't evaluate as true for undefined variables:

if (x === null) {

You can try this with various values using this example:

var a: number;
var b: number = null;

function check(x, name) {
    if (x == null) {
        console.log(name + ' == null');

    if (x === null) {
        console.log(name + ' === null');

    if (typeof x === 'undefined') {
        console.log(name + ' is undefined');

check(a, 'a');
check(b, 'b');


"a == null"

"a is undefined"

"b == null"

"b === null"

Cannot run emulator in Android Studio

It is possible that you really have no system images. Double-check that $ANDROID_HOME/system-images/android-<YOUR DESIRED API>/armeabi-v7a exists and is not empty. If they really are missing - install/reinstall with SDK manager.

ECMAScript 6 arrow function that returns an object

You must wrap the returning object literal into parentheses. Otherwise curly braces will be considered to denote the function’s body. The following works:

p => ({ foo: 'bar' });

You don't need to wrap any other expression into parentheses:

p => 10;
p => 'foo';
p => true;
p => [1,2,3];
p => null;
p => /^foo$/;

and so on.

Reference: MDN - Returning object literals

Blade if(isset) is not working Laravel

Use ?? , 'or' not supported in updated version.

{{ $usersType or '' }}  ?
{{ $usersType ?? '' }} ?

JQuery Datatables : Cannot read property 'aDataSort' of undefined

It's important that your THEAD not be empty in table.As dataTable requires you to specify the number of columns of the expected data . As per your data it should be

<table id="datatable">
            <th>Subscriber ID</th>
            <th>Install Location</th>
            <th>Subscriber Name</th>
            <th>some data</th>

React.js create loop through Array

As @Alexander solves, the issue is one of async data load - you're rendering immediately and you will not have participants loaded until the async ajax call resolves and populates data with participants.

The alternative to the solution they provided would be to prevent render until participants exist, something like this:

    render: function() {
        if (! {
            return null;
        return (
            <ul className="PlayerList">
            // I'm the Player List {}
            // <Player author="The Mini John" />
                    return <li key={player}>{player}</li>

undefined reference to 'std::cout'

Compile the program with:

g++ -Wall -Wextra -Werror -c main.cpp -o main.o
     ^^^^^^^^^^^^^^^^^^^^ <- For listing all warnings when your code is compiled.

as cout is present in the C++ standard library, which would need explicit linking with -lstdc++ when using gcc; g++ links the standard library by default.

With gcc, (g++ should be preferred over gcc)

gcc main.cpp -lstdc++ -o main.o

"undefined" function declared in another file?

go run . will run all of your files. The entry point is the function main() which has to be unique to the main package.

Another option is to build the binary with go build and run it.

Upload a file to Amazon S3 with NodeJS

Upload CSV/Excel

const fs = require('fs');
const AWS = require('aws-sdk');

const s3 = new AWS.S3({
    accessKeyId: XXXXXXXXX,
    secretAccessKey: XXXXXXXXX

const absoluteFilePath = "C:\\Project\\test.xlsx";

const uploadFile = () => {
  fs.readFile(absoluteFilePath, (err, data) => {
     if (err) throw err;
     const params = {
         Bucket: 'testBucket', // pass your bucket name
         Key: 'folderName/key.xlsx', // file will be saved in <folderName> folder
         Body: data
      s3.upload(params, function (s3Err, data) {
                    if (s3Err) throw s3Err
                    console.log(`File uploaded successfully at ${data.Location}`);


Passing Variable through JavaScript from one html page to another page

Your best option here, is to use the Query String to 'send' the value.

how to get query string value using javascript

  • So page 1 redirects to page2.html?someValue=ABC
  • Page 2 can then read the query string and specifically the key 'someValue'

If this is anything more than a learning exercise you may want to consider the security implications of this though.

Global variables wont help you here as once the page is re-loaded they are destroyed.

How do I wait for a promise to finish before returning the variable of a function?

You don't want to make the function wait, because JavaScript is intended to be non-blocking. Rather return the promise at the end of the function, then the calling function can use the promise to get the server response.

var promise = query.find(); 
return promise; 

//Or return query.find(); 

C compile : collect2: error: ld returned 1 exit status

This issue appears when you have a running console at the time you try to run other (or the same) program.

I had this problem during executing a program on Sublime Text while I had another one running on DevC++ already.

In angular $http service, How can I catch the "status" of error?

From the official angular documentation

// Simple GET request example :
  success(function(data, status, headers, config) {
    // this callback will be called asynchronously
    // when the response is available
  error(function(data, status, headers, config) {
    // called asynchronously if an error occurs
    // or server returns response with an error status.

As you can see first parameter for error callback is data an status is second.

What does "collect2: error: ld returned 1 exit status" mean?

The ld returned 1 exit status error is the consequence of previous errors. In your example there is an earlier error - undefined reference to 'clrscr' - and this is the real one. The exit status error just signals that the linking step in the build process encountered some errors. Normally exit status 0 means success, and exit status > 0 means errors.

When you build your program, multiple tools may be run as separate steps to create the final executable. In your case one of those tools is ld, which first reports the error it found (clrscr reference missing), and then it returns the exit status. Since the exit status is > 0, it means an error and is reported.

In many cases tools return as the exit status the number of errors they encountered. So if ld tool finds two errors, its exit status would be 2.

pass JSON to HTTP POST Request


var request = require('request');

var url = "http://localhost:3000";

var requestData = {

var data = {
    url: url,
    json: true,
    body: JSON.stringify(requestData)
}, function(error, httpResponse, body){

As inserting json: true option, sets body to JSON representation of value and adds "Content-type": "application/json" header. Additionally, parses the response body as JSON. LINK

UnicodeEncodeError: 'charmap' codec can't encode characters

I was getting the same UnicodeEncodeError when saving scraped web content to a file. To fix it I replaced this code:

with open(fname, "w") as f:

with this:

import io
with, "w", encoding="utf-8") as f:

Using io gives you backward compatibility with Python 2.

If you only need to support Python 3 you can use the builtin open function instead:

with open(fname, "w", encoding="utf-8") as f:

How to fix symbol lookup error: undefined symbol errors in a cluster environment

yum update

helped me out. After I had

wget: symbol lookup error: wget: undefined symbol: psl_latest

How to check if a scope variable is undefined in AngularJS template?

If you're using Angular 1, I would recommend using Angular's built-in method:


reference :

How do I setup the dotenv file in Node.js?

My code structure using is as shown below


I have required .env at the top of my app.js

import express = require('express');
import bodyParser from 'body-parser';
import mongoose = require('mongoose');

The process.env.PORT works in my app.listen function. However, on my userController file not sure how this is happening but my problem was I was getting the secretKey value and type as string when I checked using console.log() but getting undefined when trying it on jwt.sign() e.g.

console.log('Type: '+ process.env.ACCESS_TOKEN_SECRET)



jwt.sign giving error

let accessToken = jwt.sign(userObj, process.env.ACCESS_TOKEN_SECRET); //not working 

Error was

    Argument of type 'string | undefined' is not assignable to parameter of type 'Secret'.
  Type 'undefined' is not assignable to type 'Secret'.

My Solution: After reading the documentation. I required the env again in my file( which I probably should have in the first place ) and saved it to variable 'environment'

let environment = require('dotenv').config();

console logging environment this gives:

parsed: {
    DB_HOST: 'localhost',
    DB_USER: 'root',
    DB_PASS: 'pass',
    PORT: '3000',
    ACCESS_TOKEN_SECRET: 'secretKey',

Using it on jwt.sign not works

let accessToken = jwt.sign(userObj, environment.parsed.ACCESS_TOKEN_SECRET);

Hope this helps, I was stuck on it for hours. Please feel free to add anything to my answer which may help explain more on this.

How to solve Notice: Undefined index: id in C:\xampp\htdocs\invmgt\manufactured_goods\change.php on line 21

You are not getting value of $id=$_GET['id'];

And you are using it (before it gets initialised).

Use php's in built isset() function to check whether the variable is defied or not.

So, please update the line to:

$id = isset($_GET['id']) ? $_GET['id'] : '';

Undefined symbols for architecture x86_64 on Xcode 6.1

It turned out I forgot to write my @implementation part.

Xcode 6.1 Missing required architecture X86_64 in file

  • The first thing you should make sure is that your static library has all architectures. When you do a lipo -info myStaticLibrary.a on terminal - you should see armv7 armv7s i386 x86_64 arm64 architectures for your fat binary.

  • To accomplish that, I am assuming that you're making a universal binary - add the following to your architecture settings of static library project -

enter image description here

  • So, you can see that I have to manually set the Standard architectures (including 64-bit) (armv7, armv7s, arm64) of the static library project.

enter image description here

  • Alternatively, since the normal $ARCHS_STANDARD now includes 64-bit. You can also do $(ARCHS_STANDARD) and armv7s. Check lipo -info without it, and you'll figure out the missing architectures. Here's the screenshot for all architectures -

enter image description here

  • For your reference implementation (project using static library). The default settings should work fine -

    enter image description here

Update 12/03/14 Xcode 6 Standard architectures exclude armv7s.

So, armv7s is not needed? Yes. It seems that the general differences between armv7 and armv7s instruction sets are minor. So if you choose not to include armv7s, the targeted armv7 machine code still runs fine on 32 bit A6 devices, and hardly one will notice performance gap. Source

If there is a smarter way for Xcode 6.1+ (iOS 8.1 and above) - please share.

libc++abi.dylib: terminating with uncaught exception of type NSException (lldb)

It could also be wrong Segue Identifier Name. Eg -

performSegueWithIdentifier("wrongSegueName", sender: self)

How to get JSON object from Razor Model object in javascript

After use codevar json = @Html.Raw(Json.Encode(@Model.CollegeInformationlist));

You need use JSON.parse(JSON.stringify(json));

Spring: return @ResponseBody "ResponseEntity<List<JSONObject>>"

Instead of

return new ResponseEntity<JSONObject>(entities, HttpStatus.OK);


return new ResponseEntity<List<JSONObject>>(entities, HttpStatus.OK);

DataTables: Uncaught TypeError: Cannot read property 'defaults' of undefined

The problem is that dataTable is not defined at the point you are calling this method.

Ensure that you are loading the .js files in the correct order:

<script src="/Scripts/jquery.dataTables.js"></script>
<script src="/Scripts/dataTables.bootstrap.js"></script>

Proper way to set response status and JSON content in a REST API made with nodejs and express

I am using this in my Express.js application:

app.get('/', function (req, res) {
        message: 'Welcome to the project-name api'

React img tag issue with url and class

var Hello = React.createClass({
    render: function() {
      return (
        <div className="divClass">
           <img src={this.props.url} alt={`${this.props.title}'s picture`}  className="img-responsive" />
           <span>Hello {}</span>

Angularjs: Error: [ng:areq] Argument 'HomeController' is not a function, got undefined

Error: ng:areq Bad Argument has gotten me a couple times because I close the square bracket too soon. In the BAD example below it is closed incorrectly after '$state' when it should actually go before the final parenthese.


sampleApp.controller('sampleApp', ['$scope', '$state'], function($scope, $state){



sampleApp.controller('sampleApp', ['$scope', '$state', function($scope, $state){


How to use jquery $.post() method to submit form values

You have to select and send the form data as well:

    $.post("process.php", $("#reg-form").serialize(), function(data) {

Take a look at the documentation for the jQuery serialize method, which encodes the data from the form fields into a data-string to be sent to the server.

Trim whitespace from a String

Here is how you can do it:

std::string & trim(std::string & str)
   return ltrim(rtrim(str));

And the supportive functions are implemeted as:

std::string & ltrim(std::string & str)
  auto it2 =  std::find_if( str.begin() , str.end() , [](char ch){ return !std::isspace<char>(ch , std::locale::classic() ) ; } );
  str.erase( str.begin() , it2);
  return str;   

std::string & rtrim(std::string & str)
  auto it1 =  std::find_if( str.rbegin() , str.rend() , [](char ch){ return !std::isspace<char>(ch , std::locale::classic() ) ; } );
  str.erase( it1.base() , str.end() );
  return str;   

And once you've all these in place, you can write this as well:

std::string trim_copy(std::string const & str)
   auto s = str;
   return ltrim(rtrim(s));

Try this

pip is not able to install packages correctly: Permission denied error

On a Mac, you need to use this command:

STATIC_DEPS=true sudo pip install lxml

How to check if input file is empty in jQuery

To check whether the input file is empty or not by using the file length property, index should be specified like the following:

var vidFileLength = $("#videoUploadFile")[0].files.length;
if(vidFileLength === 0){
    alert("No file selected.");

How to use ng-if to test if a variable is defined

You can still use angular.isDefined()

You just need to set

$rootScope.angular = angular;

in the "run" phase.

See update plunkr:

How to pass parameters using ui-sref in ui-router to controller

You simply misspelled $stateParam, it should be $stateParams (with an s). That's why you get undefined ;)

Javascript - removing undefined fields from an object

This solution also avoids hasOwnProperty() as Object.keys returns an array of a given object's own enumerable properties.

Object.keys(obj).forEach(function (key) {
 if(typeof obj[key] === 'undefined'){
    delete obj[key];

and you can add this as null or '' for stricter cleaning.

Datatables: Cannot read property 'mData' of undefined

Slightly different problem for me from the answers given above. For me, the HTML markup was fine, but one of my columns in the javascript was missing and didn't match the html.


<table id="companies-index-table" class="table table-responsive-sm table-striped">

                                <th>Created at</th>
                                <th>Updated at</th>
                            @foreach($companies as $company)
                                    <td>{{ $company->id }}</td>
                                    <td>{{ $company->name }}</td>
                                    <td>{{ $company->created_at }}</td>
                                    <td>{{ $company->updated_at }}</td>
                                    <td>{{ $company->count }}</td>

My Script:-

        $(document).ready(function() {
                serverSide: true,
                processing: true,
                responsive: true,
                    ajax: "{{ route('admincompanies.datatables') }}",
                columns: [
                    { name: 'id' },
                    { name: 'name' },
                    { name: 'created_at' },
                    { name: 'updated_at' },     <-- I was missing this line so my columns didn't match the thead section.
                    { name: 'count', orderable: false },

Fatal error: Call to undefined function mysqli_connect()

There is no error in the, but the mysqli PHP extension is not installed on your machine. Please contact your service provider to fix this issue.

Controller not a function, got undefined, while defining controllers globally

Really great advise, except that the SAME error CAN occur simply by missing the critical script include on your root page


page: index.html



<script src="./ordersController.js"></script>

When a Route is told what controller and view to serve up:

 .when('/orders/:customerId', {
     controller: 'OrdersController',
     templateUrl: 'views/orders.html'

So essential the undefined controller issue CAN occur in this accidental mistake of not even referencing the controller!

jQuery not working with IE 11

Thanks @Arnaud & @Conny for highlighting this answer. This really helped me. I would like to add one more thing here is, adding this line <meta http-equiv="x-ua-compatible" content="IE=edge"> just after the title in tag prior to all meta tags is must for to work as it overrides the compatibility mode of IE.

How to fix PHP Warning: PHP Startup: Unable to load dynamic library 'ext\\php_curl.dll'?

As Darren commented, Apache don't understand php.ini relative paths in Windows.

To fix it, change the relative paths in your php.ini to absolute paths.


Cannot read property 'push' of undefined when combining arrays

order[] is undefined that's why

Just define order[1]...[n] to = some value

this should fix it

TypeError: Cannot read property 'then' of undefined

TypeError: Cannot read property 'then' of undefined when calling a Django service using AngularJS.

If you are calling a Python service, the code will look like below:

  var promise = $http({
    method: 'POST',
      url: bbConfig.BWS+'updateTalentSupplier/',
      withCredentials: false,
    return promise; //Promise is returned 

We are using MongoDB as the database(I know it doesn't matter. But if someone is searching with MongoDB + Python (Django) + AngularJS the result should come.

Loop through childNodes

I'm very late to the party, but since element.lastChild.nextSibling === null, the following seems like the most straightforward option to me:

for(var child=element.firstChild; child!==null; child=child.nextSibling) {

Cannot read property 'map' of undefined

The error "Cannot read property 'map' of undefined" will be encountered if there is an error in the "" or there is no array.

Better put condition to check the the array like


AngularJS - get element attributes values

function onContentLoad() {_x000D_
  var item = document.getElementById("id1");_x000D_
  var x = item.dataset.x;_x000D_
  var data = item.dataset.myData;_x000D_
  var resX = document.getElementById("resX");_x000D_
  var resData = document.getElementById("resData");_x000D_
  resX.innerText = x;_x000D_
  resData.innerText = data;_x000D_
<body onload="onContentLoad()">_x000D_
  <div id="id1" data-x="a" data-my-data="b"></div>_x000D_
  Read 'x':_x000D_
  <label id="resX"></label>_x000D_
  <br/>Read 'my-data':_x000D_
  <label id="resData"></label>_x000D_

How to check if array is empty or does not exist?

You want to do the check for undefined first. If you do it the other way round, it will generate an error if the array is undefined.

if (array === undefined || array.length == 0) {
    // array empty or does not exist


This answer is getting a fair amount of attention, so I'd like to point out that my original answer, more than anything else, addressed the wrong order of the conditions being evaluated in the question. In this sense, it fails to address several scenarios, such as null values, other types of objects with a length property, etc. It is also not very idiomatic JavaScript.

The foolproof approach
Taking some inspiration from the comments, below is what I currently consider to be the foolproof way to check whether an array is empty or does not exist. It also takes into account that the variable might not refer to an array, but to some other type of object with a length property.

if (!Array.isArray(array) || !array.length) {
  // array does not exist, is not an array, or is empty
  // ? do not attempt to process array

To break it down:

  1. Array.isArray(), unsurprisingly, checks whether its argument is an array. This weeds out values like null, undefined and anything else that is not an array.
    Note that this will also eliminate array-like objects, such as the arguments object and DOM NodeList objects. Depending on your situation, this might not be the behavior you're after.

  2. The array.length condition checks whether the variable's length property evaluates to a truthy value. Because the previous condition already established that we are indeed dealing with an array, more strict comparisons like array.length != 0 or array.length !== 0 are not required here.

The pragmatic approach
In a lot of cases, the above might seem like overkill. Maybe you're using a higher order language like TypeScript that does most of the type-checking for you at compile-time, or you really don't care whether the object is actually an array, or just array-like.

In those cases, I tend to go for the following, more idiomatic JavaScript:

if (!array || !array.length) {
    // array or array.length are falsy
    // ? do not attempt to process array

Or, more frequently, its inverse:

if (array && array.length) {
    // array and array.length are truthy
    // ? probably OK to process array

With the introduction of the optional chaining operator (Elvis operator) in ECMAScript 2020, this can be shortened even further:

if (!array?.length) {
    // array or array.length are falsy
    // ? do not attempt to process array

Or the opposite:

if (array?.length) {
    // array and array.length are truthy
    // ? probably OK to process array

Cannot get OpenCV to compile because of undefined references?

This is a linker issue. Try:

g++ -o test_1 test_1.cpp `pkg-config opencv --cflags --libs`

This should work to compile the source. However, if you recently compiled OpenCV from source, you will meet linking issue in run-time, the library will not be found. In most cases, after compiling libraries from source, you need to do finally:

sudo ldconfig

laravel foreach loop in controller

Is sku just a property of the Product model? If so:

$products = Product::whereOwnerAndStatus($owner, 0)->take($count)->get();

foreach ($products as $product ) {
  // Access $product->sku here...

Or is sku a relationship to another model? If that is the case, then, as long as your relationship is setup properly, you code should work.

Uncaught TypeError: Cannot read property 'split' of undefined

og_date = "2012-10-01";
console.log(og_date); // => "2012-10-01"

console.log(og_date.split('-')); // => [ '2012', '10', '01' ]

og_date.value would only work if the date were stored as a property on the og_date object. Such as: var og_date = {}; og_date.value="2012-10-01"; In that case, your original console.log would work.

DSO missing from command line

DSO here means Dynamic Shared Object; since the error message says it's missing from the command line, I guess you have to add it to the command line.

That is, try adding -lpthread to your command line.

Check if AJAX response data is empty/blank/null/undefined/0

This worked form me.. PHP Code on page.php

 $query_de="sql statements here";
 $sql_de = sqlsrv_query($conn,$query_de);
      if ($sql_de)
        echo "SQLSuccess";

and then AJAX Code has bellow

                    url  : "page.php",
                    type : "POST",
                    data : {
                            buttonsave   : 1,
                            var1         : val1,
                            var2         : val2,
                     if(jQuery.trim(data) === "SQLSuccess")
                           alert("Se agrego correctamente");
                          // alert(data);
                                      } else { alert(data);}
                   error: function(error)
                    alert("Error AJAX not working: "+ error );

NOTE: the word 'SQLSuccess' must be received from PHP

javascript get x and y coordinates on mouse click

simple solution is this:


document.addEventListener('click', printMousePos, true);
function printMousePos(e){

      cursorX = e.pageX;
      cursorY= e.pageY;
      $( "#test" ).text( "pageX: " + cursorX +",pageY: " + cursorY );

Uncaught TypeError: Cannot read property 'toLowerCase' of undefined

It fails "when trying to execute the function manually" because you have a different 'this'. This will refer not to the thing you have in mind when invoking the method manually, but something else, probably the window object, or whatever context object you have when invoking manually.

Node/Express file upload

Another option is to use multer, which uses busboy under the hood, but is simpler to set up.

var multer = require('multer');

Use multer and set the destination for the upload:


Create a form in your view, enctype='multipart/form-data is required for multer to work:

form(role="form", action="/", method="post", enctype="multipart/form-data")
        label Upload File
        input(type="file", name="myfile", id="myfile")

Then in your POST you can access the data about the file:'/', function(req, res) {

A full tutorial on this can be found here.

Why is my variable unaltered after I modify it inside of a function? - Asynchronous code reference

One word answer: asynchronicity.


This topic has been iterated at least a couple of thousands of times, here, in Stack Overflow. Hence, first off I'd like to point out some extremely useful resources:

The answer to the question at hand

Let's trace the common behavior first. In all examples, the outerScopeVar is modified inside of a function. That function is clearly not executed immediately, it is being assigned or passed as an argument. That is what we call a callback.

Now the question is, when is that callback called?

It depends on the case. Let's try to trace some common behavior again:

  • img.onload may be called sometime in the future, when (and if) the image has successfully loaded.
  • setTimeout may be called sometime in the future, after the delay has expired and the timeout hasn't been canceled by clearTimeout. Note: even when using 0 as delay, all browsers have a minimum timeout delay cap (specified to be 4ms in the HTML5 spec).
  • jQuery $.post's callback may be called sometime in the future, when (and if) the Ajax request has been completed successfully.
  • Node.js's fs.readFile may be called sometime in the future, when the file has been read successfully or thrown an error.

In all cases, we have a callback which may run sometime in the future. This "sometime in the future" is what we refer to as asynchronous flow.

Asynchronous execution is pushed out of the synchronous flow. That is, the asynchronous code will never execute while the synchronous code stack is executing. This is the meaning of JavaScript being single-threaded.

More specifically, when the JS engine is idle -- not executing a stack of (a)synchronous code -- it will poll for events that may have triggered asynchronous callbacks (e.g. expired timeout, received network response) and execute them one after another. This is regarded as Event Loop.

That is, the asynchronous code highlighted in the hand-drawn red shapes may execute only after all the remaining synchronous code in their respective code blocks have executed:

async code highlighted

In short, the callback functions are created synchronously but executed asynchronously. You just can't rely on the execution of an asynchronous function until you know it has executed, and how to do that?

It is simple, really. The logic that depends on the asynchronous function execution should be started/called from inside this asynchronous function. For example, moving the alerts and console.logs too inside the callback function would output the expected result, because the result is available at that point.

Implementing your own callback logic

Often you need to do more things with the result from an asynchronous function or do different things with the result depending on where the asynchronous function has been called. Let's tackle a bit more complex example:

var outerScopeVar;

function helloCatAsync() {
    setTimeout(function() {
        outerScopeVar = 'Nya';
    }, Math.random() * 2000);

Note: I'm using setTimeout with a random delay as a generic asynchronous function, the same example applies to Ajax, readFile, onload and any other asynchronous flow.

This example clearly suffers from the same issue as the other examples, it is not waiting until the asynchronous function executes.

Let's tackle it implementing a callback system of our own. First off, we get rid of that ugly outerScopeVar which is completely useless in this case. Then we add a parameter which accepts a function argument, our callback. When the asynchronous operation finishes, we call this callback passing the result. The implementation (please read the comments in order):

// 1. Call helloCatAsync passing a callback function,
//    which will be called receiving the result from the async operation
helloCatAsync(function(result) {
    // 5. Received the result from the async function,
    //    now do whatever you want with it:

// 2. The "callback" parameter is a reference to the function which
//    was passed as argument from the helloCatAsync call
function helloCatAsync(callback) {
    // 3. Start async operation:
    setTimeout(function() {
        // 4. Finished async operation,
        //    call the callback passing the result as argument
    }, Math.random() * 2000);

Code snippet of the above example:

// 1. Call helloCatAsync passing a callback function,_x000D_
//    which will be called receiving the result from the async operation_x000D_
console.log("1. function called...")_x000D_
helloCatAsync(function(result) {_x000D_
    // 5. Received the result from the async function,_x000D_
    //    now do whatever you want with it:_x000D_
    console.log("5. result is: ", result);_x000D_
// 2. The "callback" parameter is a reference to the function which_x000D_
//    was passed as argument from the helloCatAsync call_x000D_
function helloCatAsync(callback) {_x000D_
    console.log("2. callback here is the function passed as argument above...")_x000D_
    // 3. Start async operation:_x000D_
    setTimeout(function() {_x000D_
    console.log("3. start async operation...")_x000D_
    console.log("4. finished async operation, calling the callback, passing the result...")_x000D_
        // 4. Finished async operation,_x000D_
        //    call the callback passing the result as argument_x000D_
    }, Math.random() * 2000);_x000D_

Most often in real use cases, the DOM API and most libraries already provide the callback functionality (the helloCatAsync implementation in this demonstrative example). You only need to pass the callback function and understand that it will execute out of the synchronous flow, and restructure your code to accommodate for that.

You will also notice that due to the asynchronous nature, it is impossible to return a value from an asynchronous flow back to the synchronous flow where the callback was defined, as the asynchronous callbacks are executed long after the synchronous code has already finished executing.

Instead of returning a value from an asynchronous callback, you will have to make use of the callback pattern, or... Promises.


Although there are ways to keep the callback hell at bay with vanilla JS, promises are growing in popularity and are currently being standardized in ES6 (see Promise - MDN).

Promises (a.k.a. Futures) provide a more linear, and thus pleasant, reading of the asynchronous code, but explaining their entire functionality is out of the scope of this question. Instead, I'll leave these excellent resources for the interested:

More reading material about JavaScript asynchronicity

Note: I've marked this answer as Community Wiki, hence anyone with at least 100 reputations can edit and improve it! Please feel free to improve this answer, or submit a completely new answer if you'd like as well.

I want to turn this question into a canonical topic to answer asynchronicity issues which are unrelated to Ajax (there is How to return the response from an AJAX call? for that), hence this topic needs your help to be as good and helpful as possible!

Error in data frame undefined columns selected

Are you meaning?

data2 <- data1[good,]



you're selecting columns in a wrong way (using a logical vector of complete rows).

Consider that parameter pollutant is not used; is it a column name that you want to extract? if so it should be something like

data2 <- data1[good, pollutant]

Furthermore consider that you have to rbind the data.frames inside the for loop, otherwise you get only the last data.frame (its completed.cases)

And last but not least, i'd prefer generating filenames eg with

id <- 1:322
paste0( directory, "/", gsub(" ", "0", sprintf("%3d",id)), ".csv")

A little modified chunk of ?sprintf

The string fmt (in our case "%3d") contains normal characters, which are passed through to the output string, and also conversion specifications which operate on the arguments provided through .... The allowed conversion specifications start with a % and end with one of the letters in the set aAdifeEgGosxX%. These letters denote the following types:

  • d: integer

Eg a more general example

    sprintf("I am %10d years old", 25)
[1] "I am         25 years old"
          |        |
          1       10

Call angularjs function using jquery/javascript

Try this:

const scope = angular.element(document.getElementById('YourElementId')).scope();

Basic HTTP authentication with Node and Express 4

function auth (req, res, next) {
  var authHeader = req.headers.authorization;
  if (!authHeader) {
      var err = new Error('You are not authenticated!');
      res.setHeader('WWW-Authenticate', 'Basic');
      err.status = 401;
  var auth = new Buffer.from(authHeader.split(' ')[1], 'base64').toString().split(':');
  var user = auth[0];
  var pass = auth[1];
  if (user == 'admin' && pass == 'password') {
      next(); // authorized
  } else {
      var err = new Error('You are not authenticated!');
      res.setHeader('WWW-Authenticate', 'Basic');      
      err.status = 401;

jQuery: get data attribute

This works for me

$('.someclass').click(function() {
    $varName = $(this).data('fulltext');

Uncaught TypeError : cannot read property 'replace' of undefined In Grid

Please try with the below code snippet.

<!DOCTYPE html>
    <link href="" rel="stylesheet" />
    <link href="" rel="stylesheet" />
    <script src=""></script>
    <script src=""></script>
        function onDataBound(e) {
            var grid = $("#grid").data("kendoGrid");

        $(document).ready(function () {
                dataSource: {
                    type: "odata",
                    transport: {
                        read: ""
                    schema: {
                        model: {
                            fields: {
                                OrderID: { type: "number" },
                                Freight: { type: "number" },
                                ShipName: { type: "string" },
                                OrderDate: { type: "date" },
                                ShipCity: { type: "string" }
                    pageSize: 20,
                    serverPaging: true,
                    serverFiltering: true,
                    serverSorting: true
                height: 430,
                filterable: true,
                dataBound: onDataBound,
                sortable: true,
                pageable: true,
                columns: [{
                    field: "OrderID",
                    filterable: false
                                field: "OrderDate",
                                title: "Order Date",
                                width: 120,
                                format: "{0:MM/dd/yyyy}"
                            }, {
                                field: "ShipName",
                                title: "Ship Name",
                                width: 260
                            }, {
                                field: "ShipCity",
                                title: "Ship City",
                                width: 150
    <div id="grid">

I have implemented same thing with different way.

Returning a value from callback function in Node.js

Its undefined because, console.log(response) runs before doCall(urlToCall); is finished. You have to pass in a callback function aswell, that runs when your request is done.

First, your function. Pass it a callback:

function doCall(urlToCall, callback) {
    urllib.request(urlToCall, { wd: 'nodejs' }, function (err, data, response) {                              
        var statusCode = response.statusCode;
        finalData = getResponseJson(statusCode, data.toString());
        return callback(finalData);


var urlToCall = "http://myUrlToCall";
doCall(urlToCall, function(response){
    // Here you have access to your variable

@Rodrigo, posted a good resource in the comments. Read about callbacks in node and how they work. Remember, it is asynchronous code.

undefined reference to 'vtable for class' constructor

You're declaring a virtual function and not defining it:

virtual void calculateCredits();

Either define it or declare it as:

virtual void calculateCredits() = 0;

Or simply:

virtual void calculateCredits() { };

Read more about vftable:

Uncaught TypeError: undefined is not a function while using jQuery UI

The issue because of not loading jquery ui library. - CDN source file

Call above path in your file.

File uploading with Express 4.0: req.files undefined

Just to add to answers above, you can streamline the use of express-fileupload to just a single route that needs it, instead of adding it to the every route.

let fileupload = require("express-fileupload");

..."/upload", fileupload, function(req, res){



How to skip the OPTIONS preflight request?

When performing certain types of cross-domain AJAX requests, modern browsers that support CORS will insert an extra "preflight" request to determine whether they have permission to perform the action. From example query:

$http.get( ‘’ +userId,

As a result of this fragment we can see that the address was sent two requests (OPTIONS and GET). The response from the server includes headers confirming the permissibility the query GET. If your server is not configured to process an OPTIONS request properly, client requests will fail. For example:

Access-Control-Allow-Credentials: true
Access-Control-Allow-Headers: accept, origin, x-requested-with, content-type
Access-Control-Allow-Methods: DELETE
Access-Control-Allow-Methods: OPTIONS
Access-Control-Allow-Methods: PUT
Access-Control-Allow-Methods: GET
Access-Control-Allow-Methods: POST
Access-Control-Allow-Orgin: *
Access-Control-Max-Age: 172800
Allow: PUT
Allow: POST
Allow: GET

NullPointerException in eclipse in Eclipse itself at PartServiceImpl.internalFixContext

I faced the same error, but only with files cloned from git that were assigned to a proprietary plugin. I realized that even after cloning the files from git, I needed to create a new project or import a project in eclipse and this resolved the error.

How to limit the maximum value of a numeric field in a Django model?

You could also create a custom model field type - see

In this case, you could 'inherit' from the built-in IntegerField and override its validation logic.

The more I think about this, I realize how useful this would be for many Django apps. Perhaps a IntegerRangeField type could be submitted as a patch for the Django devs to consider adding to trunk.

This is working for me:

from django.db import models

class IntegerRangeField(models.IntegerField):
    def __init__(self, verbose_name=None, name=None, min_value=None, max_value=None, **kwargs):
        self.min_value, self.max_value = min_value, max_value
        models.IntegerField.__init__(self, verbose_name, name, **kwargs)
    def formfield(self, **kwargs):
        defaults = {'min_value': self.min_value, 'max_value':self.max_value}
        return super(IntegerRangeField, self).formfield(**defaults)

Then in your model class, you would use it like this (field being the module where you put the above code):

size = fields.IntegerRangeField(min_value=1, max_value=50)

OR for a range of negative and positive (like an oscillator range):

size = fields.IntegerRangeField(min_value=-100, max_value=100)

What would be really cool is if it could be called with the range operator like this:

size = fields.IntegerRangeField(range(1, 50))

But, that would require a lot more code since since you can specify a 'skip' parameter - range(1, 50, 2) - Interesting idea though...

How can I make the browser wait to display the page until it's fully loaded?

Also make sure the server buffers the page and does not immediately (while building) stream it to the client browser.

Since you have not specified your technology stack:

  • PHP: look into ob_start
  • ASP.NET: make sure Response.BufferOutput = True (it is by default)

How to include the reference of DocumentFormat.OpenXml.dll on Mono2.10?

What worked for me:

  1. Add a folder to the project call it ThirdParty.
  2. Add in the ThirdParty folder both DocumentFormat.OpenXML.dll and WindowsBase.dll
  3. Make sure the the project uses the ThirdParty dir as reference for both the DLLs
  4. Build and published to an external server.

using lodash .groupBy. how to add your own keys for grouped output?

Example groupBy and sum of a column using Lodash 4.17.4

   var data = [{
                "name": "jim",
                "color": "blue",
                "amount": 22
                }, {
                "name": "Sam",
                "color": "blue",
                "amount": 33
                }, {
               "name": "eddie",
               "color": "green",
               "amount": 77

      var result = _(data)
                   .groupBy(x => x.color)
                   .map((value, key) => 
                   ({color: key,
                    totalamount: _.sumBy(value,'amount'),
                    users: value})).value();


Change user-agent for Selenium web-driver

To build on JJC's helpful answer that builds on Louis's helpful answer...

With PhantomJS 2.1.1-windows this line works:

driver.execute_script("return navigator.userAgent")

If it doesn't work, you can still get the user agent via the log (to build on Mma's answer):

from selenium import webdriver
import json
from fake_useragent import UserAgent

dcap = dict(DesiredCapabilities.PHANTOMJS)
dcap[""] = (UserAgent().random)
driver = webdriver.PhantomJS(executable_path=r"your_path", desired_capabilities=dcap)
har = json.loads(driver.get_log('har')[0]['message']) # get the log
print('user agent: ', har['log']['entries'][0]['request']['headers'][1]['value'])

Sending HTML mail using a shell script

Another option is the sendEmail script, it also allows you to set the message type as html and include a file as the message body. See the link for details.

Specify the from user when sending email using the mail command

When sending over SMTP, the mail man page advises to set the from variable, in this way (Tested on CentOS 6):

mail -s Subject -S [email protected] [email protected]

You could also attach a file using the -a option:

mail -s Subject -S [email protected] -a path_to_attachement [email protected]

Storing and displaying unicode string (??????) using PHP and MySQL

For those who are looking for PHP ( >5.3.5 ) PDO statement, we can set charset as per below:

$dbh = new PDO('mysql:host=localhost;dbname=testdb;charset=utf8', 'username', 'password');

SSL certificate rejected trying to access GitHub over HTTPS behind firewall

I needed two things:

  1. go to cygwin setup and include the package 'ca-certificates' (it is under Net) (as indicated elsewhere).

  2. Tell git where to find the installed certificates:

    GIT_SSL_CAINFO=/usr/ssl/certs/ca-bundle.crt GIT_CURL_VERBOSE=1 git ...

    (Verbose option is not needed)

    Or storing the option permanently:

    git config --global http.sslCAinfo /usr/ssl/certs/ca-bundle.crt

    git ...

How to Apply Corner Radius to LinearLayout

try this, for Programmatically to set a background with radius to LinearLayout or any View.

 private Drawable getDrawableWithRadius() {

    GradientDrawable gradientDrawable   =   new GradientDrawable();
    gradientDrawable.setCornerRadii(new float[]{20, 20, 20, 20, 20, 20, 20, 20});
    return gradientDrawable;

LinearLayout layout = new LinearLayout(this);

<div style display="none" > inside a table not working

simply change <div> to <tbody>

<table id="authenticationSetting" style="display: none">
  <tbody id="authenticationOuterIdentityBlock" style="display: none;">
      <td class="orionSummaryHeader">
        <orion:message key="policy.wifi.enterprise.authentication.outeridentitity" />:</td>
      <td class="orionSummaryColumn">
        <orion:textbox id="authenticationOuterIdentity" size="30" />

What are the special dollar sign shell variables?

  • $_ last argument of last command
  • $# number of arguments passed to current script
  • $* / $@ list of arguments passed to script as string / delimited list

off the top of my head. Google for bash special variables.

React Router with optional path parameter

for react-router V5 and above use below syntax for multiple paths

          path={[path1, path2]}

How to change a dataframe column from String type to Double type in PySpark?

pyspark version:

  df = <source data>

  from pyspark.sql.types import *

  # Change column type
  df_new = df.withColumn("myColumn", df["myColumn"].cast(IntegerType()))

How to Programmatically Add Views to Views

This is late but this may help someone :) :) For adding the view programmatically try like

LinearLayout rlmain = new LinearLayout(this);      
LinearLayout.LayoutParams llp = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.FILL_PARENT,LinearLayout.LayoutParams.FILL_PARENT);          
LinearLayout   ll1 = new LinearLayout (this);

ImageView iv = new ImageView(this);
LinearLayout .LayoutParams lp = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.MATCH_PARENT);

setContentView(rlmain, llp);

This will create your entire view programmatcally. You can add any number of view as same. Hope this may help. :)

Python coding standards/best practices

I follow the Python Idioms and Efficiency guidelines, by Rob Knight. I think they are exactly the same as PEP 8, but are more synthetic and based on examples.

If you are using wxPython you might also want to check Style Guide for wxPython code, by Chris Barker, as well.

How to refer to Excel objects in Access VBA?

I dissent from both the answers. Don't create a reference at all, but use late binding:

  Dim objExcelApp As Object
  Dim wb As Object

  Sub Initialize()
    Set objExcelApp = CreateObject("Excel.Application")
  End Sub

  Sub ProcessDataWorkbook()
     Set wb = objExcelApp.Workbooks.Open("path to my workbook")
     Dim ws As Object
     Set ws = wb.Sheets(1)

     ws.Cells(1, 1).Value = "Hello"
     ws.Cells(1, 2).Value = "World"

     'Close the workbook
     Set wb = Nothing
  End Sub

You will note that the only difference in the code above is that the variables are all declared as objects and you instantiate the Excel instance with CreateObject().

This code will run no matter what version of Excel is installed, while using a reference can easily cause your code to break if there's a different version of Excel installed, or if it's installed in a different location.

Also, the error handling could be added to the code above so that if the initial instantiation of the Excel instance fails (say, because Excel is not installed or not properly registered), your code can continue. With a reference set, your whole Access application will fail if Excel is not installed.

How to remove specific object from ArrayList in Java?

In general an object can be removed in two ways from an ArrayList (or generally any List), by index (remove(int)) and by object (remove(Object)).

In this particular scenario: Add an equals(Object) method to your ArrayTest class. That will allow ArrayList.remove(Object) to identify the correct object.

Length of string in bash

UTF-8 string length

In addition to fedorqui's correct answer, I would like to show the difference between string length and byte length:

oLang=$LANG oLcAll=$LC_ALL
LANG=$oLang LC_ALL=$oLcAll
printf "%s is %d char len, but %d bytes len.\n" "${myvar}" $chrlen $bytlen

will render:

Généralités is 11 char len, but 14 bytes len.

you could even have a look at stored chars:

oLang=$LANG oLcAll=$LC_ALL
printf -v myreal "%q" "$myvar"
LANG=$oLang LC_ALL=$oLcAll
printf "%s has %d chars, %d bytes: (%s).\n" "${myvar}" $chrlen $bytlen "$myreal"

will answer:

Généralités has 11 chars, 14 bytes: ($'G\303\251n\303\251ralit\303\251s').

Nota: According to Isabell Cowan's comment, I've added setting to $LC_ALL along with $LANG.

Length of an argument

Argument work same as regular variables

strLen() {
    local bytlen sreal oLang=$LANG oLcAll=$LC_ALL
    printf -v sreal %q "$1"
    LANG=$oLang LC_ALL=$oLcAll
    printf "String '%s' is %d bytes, but %d chars len: %s.\n" "$1" $bytlen ${#1} "$sreal"

will work as

strLen théorème
String 'théorème' is 10 bytes, but 8 chars len: $'th\303\251or\303\250me'

Useful printf correction tool:

If you:

for string in Généralités Language Théorème Février  "Left: ?" "Yin Yang ?";do
    printf " - %-14s is %2d char length\n" "'$string'"  ${#string}

 - 'Généralités' is 11 char length
 - 'Language'     is  8 char length
 - 'Théorème'   is  8 char length
 - 'Février'     is  7 char length
 - 'Left: ?'    is  7 char length
 - 'Yin Yang ?' is 10 char length

Not really pretty... For this, there is a little function:

strU8DiffLen () { 
    local bytlen oLang=$LANG oLcAll=$LC_ALL
    LANG=$oLang LC_ALL=$oLcAll
    return $(( bytlen - ${#1} ))

Then now:

for string in Généralités Language Théorème Février  "Left: ?" "Yin Yang ?";do
    strU8DiffLen "$string"
    printf " - %-$((14+$?))s is %2d chars length, but uses %2d bytes\n" \
        "'$string'" ${#string} $((${#string}+$?))

 - 'Généralités'  is 11 chars length, but uses 14 bytes
 - 'Language'     is  8 chars length, but uses  8 bytes
 - 'Théorème'     is  8 chars length, but uses 10 bytes
 - 'Février'      is  7 chars length, but uses  8 bytes
 - 'Left: ?'      is  7 chars length, but uses  9 bytes
 - 'Yin Yang ?'   is 10 chars length, but uses 12 bytes

Unfortunely, this is not perfect!

But there left some strange UTF-8 behaviour, like double-spaced chars, zero spaced chars, reverse deplacement and other that could not be as simple...

Have a look at or for more limitations.

How to install the JDK on Ubuntu Linux

You can use oraji. It can install/uninstall both JDK or JRE from oracle java (.tar.gz).

  1. To install run sudo oraji '/path/to/the/jdk_or_jre_archive'
  2. To uninstall run oraji -u and confirm the version number.

How to make a phone call programmatically?

Solved..! September 5, 2020.

It is working very well. In this way, you do not need to have permission from user. You can open directly phone calling part.

Trick point, use ACTION_DIAL instead of ACTION_CALL.

private void callPhoneNumber() {
    String phone = "03131693169";
    Intent callIntent = new Intent(Intent.ACTION_DIAL);
    callIntent.setData(Uri.parse("tel:" + phone));

For more question, ask me on Instagram: @canerkaseler

RegEx to exclude a specific string constant

You have to use a negative lookahead assertion.


You could for example use the following.


If this does not work in your editor, try this. It is tested to work in ruby and javascript:


How to find all tables that have foreign keys that reference particular table.column and have values for those foreign keys?

1. Open phpMyAdmin
2. On the left click database name
3. On the top right corner find "Designer" tab

All constraints will be shown there.

What does the "~" (tilde/squiggle/twiddle) CSS selector mean?

General sibling combinator

The general sibling combinator selector is very similar to the adjacent sibling combinator selector. The difference is that the element being selected doesn't need to immediately succeed the first element, but can appear anywhere after it.

More info

How to remove new line characters from data rows in mysql?

your syntax is wrong:

update mytable SET title = TRIM(TRAILING '\n' FROM title)


If the newline character is at the start of the field:

update mytable SET title = TRIM(LEADING '\n' FROM title)

SELECT list is not in GROUP BY clause and contains nonaggregated column .... incompatible with sql_mode=only_full_group_by

> sudo nano /etc/mysql/my.cnf

Enter below

sql_mode = ""

Ctrl + O => Y = Ctrl + X

> sudo service mysql restart

How to start rails server?

I believe this is what happens if "rails new [project]" has not actually executed correctly. If you are doing this on windows and "rails server" just returns the help screen, you may need to restart your command prompt window and likely repeat your setup instructions. This is more likely true if this is your first time setting up the environment.

Using Linq select list inside list

list.Where(m => m.application == "applicationName" && 
           m.users.Any(u => u.surname=="surname"));

if you want to filter users as TimSchmelter commented, you can use

list.Where(m => m.application == "applicationName")
    .Select(m => new Model
        application = m.application,
        users = m.users.Where(u => u.surname=="surname").ToList()

difference between $query>num_rows() and $this->db->count_all_results() in CodeIgniter & which one is recommended

With num_rows() you first perform the query, and then you can check how many rows you got. count_all_results() on the other hand only gives you the number of rows your query would produce, but doesn't give you the actual resultset.

// num rows example
$query = $this->db->get('table');
$num = $query->num_rows();
// here you can do something with $query

// count all example
$num = $this->db->count_all_results('table');
// here you only have $num, no $query

Getting results between two dates in PostgreSQL

You have to use the date part fetching method:

SELECT * FROM testbed WHERE start_date  ::date >= to_date('2012-09-08' ,'YYYY-MM-DD') and date::date <= to_date('2012-10-09' ,'YYYY-MM-DD')

JavaScript: IIF like statement

I typed this in my URL bar:

javascript:{ var col = 'screwdriver'; var x = '<option value="' + col + '"' + ((col == 'screwdriver') ? ' selected' : '') + '>Very roomy</option>'; alert(x); }

IEnumerable<object> a = new IEnumerable<object>(); Can I do this?

No, You cannot do that. Use the following line of code instead:

IEnumerable<int> usersIds = new List<int>() {1, 2, 3}.AsEnumerable();

I hope it helps.

How to kill all processes with a given partial name?

I took Eugen Rieck's answer and worked with it. My code adds the following:

  1. ps ax includes grep, so I excluded it with grep -Eiv 'grep'
  2. Added a few ifs and echoes to make it human-readable.

I've created a file, named it killserver, here it goes:

PROCESS_LIST=`ps ax | grep -Ei ${PROCESS_TO_KILL} | grep -Eiv 'grep' | awk ' { print $1;}'`
  if [ ! -z $KILLPID ];then
    kill -9 $KILLPID
    echo "Killed PID ${KILLPID}"

if [ -z $KILLED ];then
    echo "Didn't kill anything"


?  myapp git:(master) bash killserver
Killed PID 3358
Killed PID 3382
?  myapp git:(master) bash killserver
Didn't kill anything

Add floating point value to android resources/values

As described in this link

Declare in dimen.xml

<item name="my_float_value" type="dimen" format="float">9.52</item>

Referencing from xml


Referencing from java

TypedValue typedValue = new TypedValue();
getResources().getValue(R.dimen.my_float_value, typedValue, true);
float myFloatValue = typedValue.getFloat();

Reading input files by line using read command in shell scripting skips last line

One line answer:

IFS=$'\n'; for line in $(cat file.txt); do echo "$line" ; done

Create a new RGB OpenCV image using Python?

The new cv2 interface for Python integrates numpy arrays into the OpenCV framework, which makes operations much simpler as they are represented with simple multidimensional arrays. For example, your question would be answered with:

import cv2  # Not actually necessary if you just want to create an image.
import numpy as np
blank_image = np.zeros((height,width,3), np.uint8)

This initialises an RGB-image that is just black. Now, for example, if you wanted to set the left half of the image to blue and the right half to green , you could do so easily:

blank_image[:,0:width//2] = (255,0,0)      # (B, G, R)
blank_image[:,width//2:width] = (0,255,0)

If you want to save yourself a lot of trouble in future, as well as having to ask questions such as this one, I would strongly recommend using the cv2 interface rather than the older cv one. I made the change recently and have never looked back. You can read more about cv2 at the OpenCV Change Logs.

How to select all elements with a particular ID in jQuery?

Your document should not contain two divs with the same id. This is invalid HTML, and as a result, the underlying DOM API does not support it.

From the HTML standard:

id = name [CS] This attribute assigns a name to an element. This name must be unique in a document.

You can either assign different ids to each div and select them both using $('#id1, #id2). Or assign the same class to both elements (.cls for example), and use $('.cls') to select them both.

HTML.ActionLink vs Url.Action in ASP.NET Razor

Yes, there is a difference. Html.ActionLink generates an <a href=".."></a> tag whereas Url.Action returns only an url.

For example:

@Html.ActionLink("link text", "someaction", "somecontroller", new { id = "123" }, null)


<a href="/somecontroller/someaction/123">link text</a>

and Url.Action("someaction", "somecontroller", new { id = "123" }) generates:


There is also Html.Action which executes a child controller action.

How to "wait" a Thread in Android

I just add this line exactly as it appears below (if you need a second delay):

try {
} catch(InterruptedException e) {
    // Process exception

I find the catch IS necessary (Your app can crash due to Android OS as much as your own code).

Write a file in UTF-8 using FileWriter (Java)?

Since Java 11 you can do:

FileWriter fw = new FileWriter("filename.txt", Charset.forName("utf-8"));

How to edit CSS style of a div using C# in .NET

Add runat to the element in the markup

<div id="formSpinner" runat="server">
    <img src="images/spinner.gif">

Then you can get to the control's class attributes by using formSpinner.Attributes("class") It will only be a string, but you should be able to edit it.

cancelling a handler.postdelayed process

In case you do have multiple inner/anonymous runnables passed to same handler, and you want to cancel all at same event use


As per documentation,

Remove any pending posts of callbacks and sent messages whose obj is token. If token is null, all callbacks and messages will be removed.

Open fancybox from function

The answers seems a bit over complicated. I hope I didn't misunderstand the question.

If you simply want to open a fancy box from a click to an "A" tag. Just set your html to

<a id="my_fancybox" href="#contentdiv">click me</a>

The contents of your box will be inside of a div with id "contentdiv" and in your javascript you can initialize fancybox like this:

    'autoScale': true,
    'transitionIn': 'elastic',
    'transitionOut': 'elastic',
    'speedIn': 500,
    'speedOut': 300,
    'autoDimensions': true,
    'centerOnScroll': true,

This will show a fancybox containing "contentdiv" when your anchor tag is clicked.

How to find the length of an array in shell?

In the Fish Shell the length of an array can be found with:

$ set a 1 2 3 4
$ count $a

'xmlParseEntityRef: no name' warnings while loading xml into a php file

This solve my problème:

$description = strip_tags($value['Description']);
$description=preg_replace('/&(?!#?[a-z0-9]+;)/', '&amp;', $description);
$description= preg_replace("/(^[\r\n]*|[\r\n]+)[\s\t]*[\r\n]+/", "\n", $description);
$description=str_replace(' & ', ' &amp; ', html_entity_decode((htmlspecialchars_decode($description))));

Change action bar color in android

Maybe this can help you also. It's from the website:

First things first you need to have a custom theme declared for your application (or activity, depending on your needs). Something like…

<!-- Somewhere in AndroidManifest.xml -->
<application ... android:theme="@style/ThemeSelector">

Then, declare your custom theme for two cases, API versions with and without the Holo Themes. For the old themes we’ll customize the windowTitleBackgroundStyle attribute, and for the newer ones the ActionBarStyle.

<!-- res/values/styles.xml -->
<?xml version="1.0" encoding="utf-8"?>

    <style name="ThemeSelector" parent="android:Theme.Light">
        <item name="android:windowTitleBackgroundStyle">@style/WindowTitleBackground</item>

    <style name="WindowTitleBackground">     
        <item name="android:background">@color/title_background</item>


<!-- res/values-v11/styles.xml -->
<?xml version="1.0" encoding="utf-8"?>

    <style name="ThemeSelector" parent="android:Theme.Holo.Light">
        <item name="android:actionBarStyle">@style/ActionBar</item>

    <style name="ActionBar" parent="android:style/Widget.Holo.ActionBar">     
        <item name="android:background">@color/title_background</item>


That’s it!

Set timeout for webClient.DownloadFile()

Try WebClient.DownloadFileAsync(). You can call CancelAsync() by timer with your own timeout.

Increasing the JVM maximum heap size for memory intensive applications

I believe the 2GB limit is for 32-bit Java. I thought v1.6 was always 64 bit, but try forcing 64 bit mode just to see: add the -d64 option.

How to trigger checkbox click event even if it's checked through Javascript code?

You can use the jQuery .trigger() method. See



React JS get current date

Your problem is that you are naming your component class Date. When you call new Date() within your class, it won't create an instance of the Date you expect it to create (which is likely this Date)- it will try to create an instance of your component class. Then the constructor will try to create another instance, and another instance, and another instance... Until you run out of stack space and get the error you're seeing.

If you want to use Date within your class, try naming your class something different such as Calendar or DateComponent.

The reason for this is how JavaScript deals with name scope: Whenever you create a new named entity, if there is already an entity with that name in scope, that name will stop referring to the previous entity and start referring to your new entity. So if you use the name Date within a class named Date, the name Date will refer to that class and not to any object named Date which existed before the class definition started.

Calling Scalar-valued Functions in SQL

Can do the following

PRINT dbo.[FunctionName] ( [Parameter/Argument] )


PRINT dbo.StringSplit('77,54')

Single huge .css file vs. multiple smaller specific .css files?

Historically, one of the main advantages x in having a single CSS file is the speed benefit when using HTTP1.1.

However, as of March 2018 over 80% of browsers now support HTTP2 which allows the browser to download multiple resources simultaneously as well as being able to push resources pre-emptively. Having a single CSS file for all pages means a larger than necessary file size. With proper design, I don't see any advantage in doing this other than its easier to code.

The ideal design for HTTP2 for best performance would be:

  • Have a core CSS file which contains common styles used across all pages.
  • Have page specific CSS in a separate file
  • Use HTTP2 push CSS to minimise wait time (a cookie can be used to prevent repeated pushes)
  • Optionally separate above the fold CSS and push this first and load the remaining CSS later (useful for low-bandwidth mobile devices)
  • You could also load remaining CSS for the site or specific pages after the page has loaded if you want to speed up future page loads.

Is it valid to define functions in JSON results?

Leave the quotes off...

var a = {"b":function(){alert('hello world');} };


Download file from web in Python 3

You can use wget which is popular downloading shell tool for that. This will be the simplest method since it does not need to open up the destination file. Here is an example.

import wget
url = '', '/Users/scott/Downloads/cat4.jpg') 

test attribute in JSTL <c:if> tag

You can also use something like

<c:if test="${ testObject.testPropert == "testValue" }">...</c:if>

Getting parts of a URL (Regex)

I was trying to solve this in javascript, which should be handled by:

var url = new URL('http://a:[email protected]:890/path/wah@t/foo.js?foo=bar&bingobang=&[email protected]#foobar/bing/bo@ng?bang');

since (in Chrome, at least) it parses to:

  "hash": "#foobar/bing/bo@ng?bang",
  "search": "?foo=bar&bingobang=&[email protected]",
  "pathname": "/path/wah@t/foo.js",
  "port": "890",
  "hostname": "",
  "host": "",
  "password": "b",
  "username": "a",
  "protocol": "http:",
  "origin": "",
  "href": "http://a:[email protected]:890/path/wah@t/foo.js?foo=bar&bingobang=&[email protected]#foobar/bing/bo@ng?bang"

However, this isn't cross browser (, so I cobbled this together to pull the same parts out as above:


Credit for this regex goes to who posted this jsperf (originally found here: who came up with the regex this was originally based on.

The parts are in this order:

var keys = [
    "href",                    // http://user:[email protected]:81/directory/file.ext?query=1#anchor
    "origin",                  // http://user:[email protected]:81
    "protocol",                // http:
    "username",                // user
    "password",                // pass
    "host",                    //
    "hostname",                //
    "port",                    // 81
    "pathname",                // /directory/file.ext
    "search",                  // ?query=1
    "hash"                     // #anchor

There is also a small library which wraps it and provides query params: (also available on bower)

If you have an improvement, please create a pull request with more tests and I will accept and merge with thanks.

Changing the Git remote 'push to' default

In my case, I fixed by the following: * run git config --edit * In the git config file:

[branch "master"]
remote = origin # <--- change the default origin here

Sum all the elements java arraylist

Java 8+ version for Integer, Long, Double and Float

    List<Integer> ints = Arrays.asList(1, 2, 3, 4, 5);
    List<Long> longs = Arrays.asList(1L, 2L, 3L, 4L, 5L);
    List<Double> doubles = Arrays.asList(1.2d, 2.3d, 3.0d, 4.0d, 5.0d);
    List<Float> floats = Arrays.asList(1.3f, 2.2f, 3.0f, 4.0f, 5.0f);

    long intSum =

    long longSum =

    double doublesSum =

    double floatsSum =

            "Integers: %s, Longs: %s, Doubles: %s, Floats: %s",
            intSum, longSum, doublesSum, floatsSum));

15, 15, 15.5, 15.5

Difference between JPanel, JFrame, JComponent, and JApplet

Those classes are common extension points for Java UI designs. First off, realize that they don't necessarily have much to do with each other directly, so trying to find a relationship between them might be counterproductive.

JApplet - A base class that let's you write code that will run within the context of a browser, like for an interactive web page. This is cool and all but it brings limitations which is the price for it playing nice in the real world. Normally JApplet is used when you want to have your own UI in a web page. I've always wondered why people don't take advantage of applets to store state for a session so no database or cookies are needed.

JComponent - A base class for objects which intend to interact with Swing.

JFrame - Used to represent the stuff a window should have. This includes borders (resizeable y/n?), titlebar (App name or other message), controls (minimize/maximize allowed?), and event handlers for various system events like 'window close' (permit app to exit yet?).

JPanel - Generic class used to gather other elements together. This is more important with working with the visual layout or one of the provided layout managers e.g. gridbaglayout, etc. For example, you have a textbox that is bigger then the area you have reserved. Put the textbox in a scrolling pane and put that pane into a JPanel. Then when you place the JPanel, it will be more manageable in terms of layout.

Can I access a form in the controller?

Bit late for an answer but came with following option. It is working for me but not sure if it is the correct way or not.

In my view I'm doing this:

<form name="formName">
    <div ng-init="setForm(formName);"></div>

And in the controller:

$scope.setForm = function (form) {
    $scope.myForm = form;

Now after doing this I have got my form in my controller variable which is $scope.myForm

Xcode warning: "Multiple build commands for output file"

Commenting use_frameworks! in PodFile worked for me.


Note: Did this on XCode 10.1, pod version 1.8.4

jQuery scroll to element

To show the full element (if it's possible with the current window size):

var element       = $("#some_element");
var elementHeight = element.height();
var windowHeight  = $(window).height();

var offset = Math.min(elementHeight, windowHeight) + element.offset().top;
$('html, body').animate({ scrollTop: offset }, 500);

Make a directory and copy a file

You can use the shell for this purpose.

Set shl = CreateObject("WScript.Shell") 
shl.Run "cmd mkdir YourDir" & copy "

Codeigniter $this->db->order_by(' ','desc') result is not complete

Put from before where, and order_by on last:


Or try BINARY:


You should add manually on codeigniter for binary sorting.

And set "course_name" character column.

If sorting is used on a character type column, normally the sort is conducted in a case-insensitive fashion.

What type of structure data in courses table?

If you frustrated you can put into array and return using PHP:

Use natcasesort for order in "natural order": (Reference:

Your array from database as example: $array_db = $result_from_db:

$final_result = natcasesort($array_db);


EOFException - how to handle?

The best way to handle this would be to terminate your infinite loop with a proper condition.

But since you asked for the exception handling:

Try to use two catches. Your EOFException is expected, so there seems to be no problem when it occures. Any other exception should be handled.

} catch (EOFException e) {
   // ... this is fine
} catch(IOException e) {
    // handle exception which is not expected

Best way to define private methods for a class in Objective-C

You could try defining a static function below or above your implementation that takes a pointer to your instance. It will be able to access any of your instances variables.

//.h file
@interface MyClass : Object
    int test;
- (void) someMethod: anArg;


//.m file    
@implementation MyClass

static void somePrivateMethod (MyClass *myClass, id anArg)
    fprintf (stderr, "MyClass (%d) was passed %p", myClass->test, anArg);

- (void) someMethod: (id) anArg
    somePrivateMethod (self, anArg);


requestFeature() must be called before adding content

For SDK version 23 and above, the same RuntimeException is thrown if you are using AppCompatActivity to extend your activity. It will not happen if your activity derives directly from Activity.

This is a known issue on google as mentioned in

The work around provided for this is to use supportRequestWindowFeature() method instead of using requestFeature().

Please upvote if it solves your problem.

Changing directory in Google colab (breaking out of the python interpreter)

As others have pointed out, the cd command needs to start with a percentage sign:

%cd SwitchFrequencyAnalysis

Difference between % and !

Google Colab seems to inherit these syntaxes from Jupyter (which inherits them from IPython). Jake VanderPlas explains this IPython behaviour here. You can see the excerpt below.

If you play with IPython's shell commands for a while, you might notice that you cannot use !cd to navigate the filesystem:

In [11]: !pwd 

In [12]: !cd ..

In [13]: !pwd 

The reason is that shell commands in the notebook are executed in a temporary subshell. If you'd like to change the working directory in a more enduring way, you can use the %cd magic command:

In [14]: %cd ..

Another way to look at this: you need % because changing directory is relevant to the environment of the current notebook but not to the entire server runtime.

In general, use ! if the command is one that's okay to run in a separate shell. Use % if the command needs to be run on the specific notebook.

Polymorphism: Why use "List list = new ArrayList" instead of "ArrayList list = new ArrayList"?

This is called programming to interface. This will be helpful in case if you wish to move to some other implementation of List in the future. If you want some methods in ArrayList then you would need to program to the implementation that is ArrayList a = new ArrayList().

How to set IE11 Document mode to edge as default?

unchecked the "Automatically detect settings" in the Local Area Network Settings (found in "Internet Options" > Connections > LAN Settings.

JQuery .each() backwards

I present you with the cleanest way ever, in the form of the world's smallest jquery plugin:

jQuery.fn.reverse = [].reverse;


$('jquery-selectors-go-here').reverse().each(function () {
    //business as usual goes here

-All credit to Michael Geary in his post here:[email protected]/msg04261.html

Entity Framework 6 Code first Default value

After @SedatKapanoglu comment, I am adding all my approach that works, because he was right, just using the fluent API does not work.

1- Create custom code generator and override Generate for a ColumnModel.

   public class ExtendedMigrationCodeGenerator : CSharpMigrationCodeGenerator

    protected override void Generate(ColumnModel column, IndentedTextWriter writer, bool emitName = false)

        if (column.Annotations.Keys.Contains("Default"))
            var value = Convert.ChangeType(column.Annotations["Default"].NewValue, column.ClrDefaultValue.GetType());
            column.DefaultValue = value;

        base.Generate(column, writer, emitName);


2- Assign the new code generator:

public sealed class Configuration : DbMigrationsConfiguration<Data.Context.EfSqlDbContext>
    public Configuration()
        CodeGenerator = new ExtendedMigrationCodeGenerator();
        AutomaticMigrationsEnabled = false;

3- Use fluent api to created the Annotation:

public static void Configure(DbModelBuilder builder){    
builder.Entity<Company>().Property(c => c.Status).HasColumnAnnotation("Default", 0);            

SpringMVC RequestMapping for GET parameters

If you are willing to change your uri, you could also use PathVariable.

@RequestMapping(value="/mapping/foo/{foo}/{bar}", method=RequestMethod.GET)
public String process(@PathVariable String foo,@PathVariable String bar) {
    //Perform logic with foo and bar

NB: The first foo is part of the path, the second one is the PathVariable

Difference between text and varchar (character varying)

On PostgreSQL manual

There is no performance difference among these three types, apart from increased storage space when using the blank-padded type, and a few extra CPU cycles to check the length when storing into a length-constrained column. While character(n) has performance advantages in some other database systems, there is no such advantage in PostgreSQL; in fact character(n) is usually the slowest of the three because of its additional storage costs. In most situations text or character varying should be used instead.

I usually use text


What does %s mean in a python format string?

%sand %d are Format Specifiers or placeholders for formatting strings/decimals/floats etc.

MOST common used Format specifier:

%s : string

%d : decimals

%f : float

Self explanatory code:

name = "Gandalf"
extendedName = "the Grey"
age = 84
IQ = 149.9
print('type(name):', type(name)) #type(name): <class 'str'>
print('type(age):', type(age))   #type(age): <class 'int'>   
print('type(IQ):', type(IQ))     #type(IQ): <class 'float'>   

print('%s %s\'s age is %d with incredible IQ of %f ' %(name, extendedName, age, IQ)) #Gandalf the Grey's age is 84 with incredible IQ of 149.900000 

#Same output can be printed in following ways:

print ('{0} {1}\'s age is {2} with incredible IQ of {3} '.format(name, extendedName, age, IQ))          # with help of older method
print ('{} {}\'s age is {} with incredible IQ of {} '.format(name, extendedName, age, IQ))          # with help of older method

print("Multiplication of %d and %f is %f" %(age, IQ, age*IQ)) #Multiplication of 84 and 149.900000 is 12591.600000          

#storing formattings in string

sub1 = "python string!"
sub2 = "an arg"

a = "i am a %s" % sub1
b = "i am a {0}".format(sub1)

c = "with %(kwarg)s!" % {'kwarg':sub2}
d = "with {kwarg}!".format(kwarg=sub2)

print(a)    # "i am a python string!"
print(b)   # "i am a python string!"
print(c)    # "with an arg!"
print(d)   # "with an arg!"

jQuery: more than one handler for same event

Both handlers will run, the jQuery event model allows multiple handlers on one element, therefore a later handler does not override an older handler.

The handlers will execute in the order in which they were bound.

How do I determine the size of an object in Python?

Having run into this problem many times myself, I wrote up a small function (inspired by @aaron-hall's answer) & tests that does what I would have expected sys.getsizeof to do:

If you're interested in the backstory, here it is

EDIT: Attaching the code below for easy reference. To see the most up-to-date code, please check the github link.

    import sys

    def get_size(obj, seen=None):
        """Recursively finds size of objects"""
        size = sys.getsizeof(obj)
        if seen is None:
            seen = set()
        obj_id = id(obj)
        if obj_id in seen:
            return 0
        # Important mark as seen *before* entering recursion to gracefully handle
        # self-referential objects
        if isinstance(obj, dict):
            size += sum([get_size(v, seen) for v in obj.values()])
            size += sum([get_size(k, seen) for k in obj.keys()])
        elif hasattr(obj, '__dict__'):
            size += get_size(obj.__dict__, seen)
        elif hasattr(obj, '__iter__') and not isinstance(obj, (str, bytes, bytearray)):
            size += sum([get_size(i, seen) for i in obj])
        return size

Custom style to jquery ui dialogs

The solution only solves part of the problem, it may let you style the container and contents but doesn't let you change the titlebar. I developed a workaround of sorts but adding an id to the dialog div, then using jQuery .prev to change the style of the div which is the previous sibling of the dialog's div. This works because when jQueryUI creates the dialog, your original div becomes a sibling of the new container, but the title div is a the immediately previous sibling to your original div but neither the container not the title div has an id to simplify selecting the div.


<button id="dialog1" class="btn btn-danger">Warning</button>
<div title="Nothing here, really" id="nonmodal1">
  Nothing here

You can use CSS to style the main section of the dialog but not the title

.custom-ui-widget-header-warning {
  background: #EBCCCC;
  font-size: 1em;

You need some JS to style the title

$(function() {
                     minWidth: 400,
                     minHeight: 'auto',
                     autoOpen: false,
                     dialogClass: 'custom-ui-widget-header-warning',
                     position: {
                       my: 'center',
                       at: 'left'

                   $("#dialog1").click(function() {
                     if ($("#nonmodal1").dialog("isOpen") === true) {
                     } else {


The example only shows simple styling (background) but you can make it as complex as you wish.

You can see it in action here:

PHPMailer AddAddress()

All answers are great. Here is an example use case for multiple add address: The ability to add as many email you want on demand with a web form:

See it in action with jsfiddle here (except the php processor)

### Send unlimited email with a web form
# Form for continuously adding e-mails:
<button type="button" onclick="emailNext();">Click to Add Another Email.</button>
<div id="addEmail"></div>
<button type="submit">Send All Emails</button>
# Script function:
function emailNext() {
    var nextEmail, inside_where;
    nextEmail = document.createElement('input');
    nextEmail.type = 'text'; = 'emails[]';
    nextEmail.className = 'class_for_styling'; = 'block';
    nextEmail.placeholder  = 'Enter E-mail Here';
    inside_where = document.getElementById('addEmail');
    return false;
# PHP Data Processor:
// ...
// Add the rest of your $mailer here...
if ($_POST[emails]){
    foreach ($_POST[emails] AS $postEmail){
        if ($postEmail){$mailer->AddAddress($postEmail);}

So what it does basically is to generate a new input text box on every click with the name "emails[]".

The [] added at the end makes it an array when posted.

Then we go through each element of the array with "foreach" on PHP side adding the:


Replace non-numeric with empty string

Using the Regex methods in .NET you should be able to match any non-numeric digit using \D, like so:

phoneNumber  = Regex.Replace(phoneNumber, "\\D", String.Empty);

How to increment a pointer address and pointer's value?

With regards to "How to increment a pointer address and pointer's value?" I think that ++(*p++); is actually well defined and does what you're asking for, e.g.:

#include <stdio.h>

int main() {
  int a = 100;
  int *p = &a;
  return 0;

It's not modifying the same thing twice before a sequence point. I don't think it's good style though for most uses - it's a little too cryptic for my liking.

css absolute position won't work with margin-left:auto margin-right: auto

Working JSFiddle below. When using position absolute, margin: 0 auto will not work, but you can do like this (will also scale):

left: 50%;
transform: translateX(-50%);

Update: Working JSFiddle

Task vs Thread differences



Thread represents an actual OS-level thread, with its own stack and kernel resources. (technically, a CLR implementation could use fibers instead, but no existing CLR does this) Thread allows the highest degree of control; you can Abort() or Suspend() or Resume() a thread (though this is a very bad idea), you can observe its state, and you can set thread-level properties like the stack size, apartment state, or culture.

The problem with Thread is that OS threads are costly. Each thread you have consumes a non-trivial amount of memory for its stack, and adds additional CPU overhead as the processor context-switch between threads. Instead, it is better to have a small pool of threads execute your code as work becomes available.

There are times when there is no alternative Thread. If you need to specify the name (for debugging purposes) or the apartment state (to show a UI), you must create your own Thread (note that having multiple UI threads is generally a bad idea). Also, if you want to maintain an object that is owned by a single thread and can only be used by that thread, it is much easier to explicitly create a Thread instance for it so you can easily check whether code trying to use it is running on the correct thread.


ThreadPool is a wrapper around a pool of threads maintained by the CLR. ThreadPool gives you no control at all; you can submit work to execute at some point, and you can control the size of the pool, but you can't set anything else. You can't even tell when the pool will start running the work you submit to it.

Using ThreadPool avoids the overhead of creating too many threads. However, if you submit too many long-running tasks to the threadpool, it can get full, and later work that you submit can end up waiting for the earlier long-running items to finish. In addition, the ThreadPool offers no way to find out when a work item has been completed (unlike Thread.Join()), nor a way to get the result. Therefore, ThreadPool is best used for short operations where the caller does not need the result.


Finally, the Task class from the Task Parallel Library offers the best of both worlds. Like the ThreadPool, a task does not create its own OS thread. Instead, tasks are executed by a TaskScheduler; the default scheduler simply runs on the ThreadPool.

Unlike the ThreadPool, Task also allows you to find out when it finishes, and (via the generic Task) to return a result. You can call ContinueWith() on an existing Task to make it run more code once the task finishes (if it's already finished, it will run the callback immediately). If the task is generic, ContinueWith() will pass you the task's result, allowing you to run more code that uses it.

You can also synchronously wait for a task to finish by calling Wait() (or, for a generic task, by getting the Result property). Like Thread.Join(), this will block the calling thread until the task finishes. Synchronously waiting for a task is usually bad idea; it prevents the calling thread from doing any other work, and can also lead to deadlocks if the task ends up waiting (even asynchronously) for the current thread.

Since tasks still run on the ThreadPool, they should not be used for long-running operations, since they can still fill up the thread pool and block new work. Instead, Task provides a LongRunning option, which will tell the TaskScheduler to spin up a new thread rather than running on the ThreadPool.

All newer high-level concurrency APIs, including the Parallel.For*() methods, PLINQ, C# 5 await, and modern async methods in the BCL, are all built on Task.


The bottom line is that Task is almost always the best option; it provides a much more powerful API and avoids wasting OS threads.

The only reasons to explicitly create your own Threads in modern code are setting per-thread options, or maintaining a persistent thread that needs to maintain its own identity.

Check for null variable in Windows batch

Late answer, but currently the accepted one is at least suboptimal.

Using quotes is ALWAYS better than using any other characters to enclose %1.
Because when %1 contains spaces or special characters like &, the IF [%1] == simply stops with a syntax error.

But for the case that %1 contains quotes, like in myBatch.bat "my file.txt", a simple IF "%1" == "" would fail.

But as you can't know if quotes are used or not, there is the syntax %~1, this removes enclosing quotes when necessary.

Therefore, the code should look like

set "file1=%~1"
IF "%~1"=="" set "file1=default file"

type "%file1%"   --- always enclose your variables in quotes

If you have to handle stranger and nastier arguments like myBatch.bat "This & will "^&crash
Then take a look at SO:How to receive even the strangest command line parameters?

Fill drop down list on selection of another drop down list

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namespace MvcApplicationrazor.Models
    public class CountryModel
        public List<State> StateModel { get; set; }
        public SelectList FilteredCity { get; set; }
    public class State
        public int Id { get; set; }
        public string StateName { get; set; }
    public class City
        public int Id { get; set; }
        public int StateId { get; set; }
        public string CityName { get; set; }


public ActionResult Index()
            CountryModel objcountrymodel = new CountryModel();
            objcountrymodel.StateModel = new List<State>();
            objcountrymodel.StateModel = GetAllState();
            return View(objcountrymodel);

        //Action result for ajax call
        public ActionResult GetCityByStateId(int stateid)
            List<City> objcity = new List<City>();
            objcity = GetAllCity().Where(m => m.StateId == stateid).ToList();
            SelectList obgcity = new SelectList(objcity, "Id", "CityName", 0);
            return Json(obgcity);
        // Collection for state
        public List<State> GetAllState()
            List<State> objstate = new List<State>();
            objstate.Add(new State { Id = 0, StateName = "Select State" });
            objstate.Add(new State { Id = 1, StateName = "State 1" });
            objstate.Add(new State { Id = 2, StateName = "State 2" });
            objstate.Add(new State { Id = 3, StateName = "State 3" });
            objstate.Add(new State { Id = 4, StateName = "State 4" });
            return objstate;
        //collection for city
        public List<City> GetAllCity()
            List<City> objcity = new List<City>();
            objcity.Add(new City { Id = 1, StateId = 1, CityName = "City1-1" });
            objcity.Add(new City { Id = 2, StateId = 2, CityName = "City2-1" });
            objcity.Add(new City { Id = 3, StateId = 4, CityName = "City4-1" });
            objcity.Add(new City { Id = 4, StateId = 1, CityName = "City1-2" });
            objcity.Add(new City { Id = 5, StateId = 1, CityName = "City1-3" });
            objcity.Add(new City { Id = 6, StateId = 4, CityName = "City4-2" });
            return objcity;


@model MvcApplicationrazor.Models.CountryModel
    ViewBag.Title = "Index";
    Layout = "~/Views/Shared/_Layout.cshtml";

<script src=""></script>
<script language="javascript" type="text/javascript">
    function GetCity(_stateId) {
        var procemessage = "<option value='0'> Please wait...</option>";
        var url = "/Test/GetCityByStateId/";

            url: url,
            data: { stateid: _stateId },
            cache: false,
            type: "POST",
            success: function (data) {
                var markup = "<option value='0'>Select City</option>";
                for (var x = 0; x < data.length; x++) {
                    markup += "<option value=" + data[x].Value + ">" + data[x].Text + "</option>";
            error: function (reponse) {
                alert("error : " + reponse);

 MVC Cascading Dropdown List Using Jquery</h4>
@using (Html.BeginForm())
    @Html.DropDownListFor(m => m.StateModel, new SelectList(Model.StateModel, "Id", "StateName"), new { @id = "ddlstate", @style = "width:200px;", @onchange = "javascript:GetCity(this.value);" })
    <br />
    <br />
    <select id="ddlcity" name="ddlcity" style="width: 200px">


    <br /><br />

jQuery bind to Paste Event, how to get the content of the paste

It would appear as though this event has some clipboardData property attached to it (it may be nested within the originalEvent property). The clipboardData contains an array of items and each one of those items has a getAsString() function that you can call. This returns the string representation of what is in the item.

Those items also have a getAsFile() function, as well as some others which are browser specific (e.g. in webkit browsers, there is a webkitGetAsEntry() function).

For my purposes, I needed the string value of what is being pasted. So, I did something similar to this:

$(element).bind("paste", function (e) {
    e.originalEvent.clipboardData.items[0].getAsString(function (pStringRepresentation) {
        // pStringRepresentation now contains the string representation of what was pasted.
        // This does not include HTML or any markup. Essentially jQuery's $(element).text()
        // function result.

You'll want to perform an iteration through the items, keeping a string concatenation result.

The fact that there is an array of items makes me think more work will need to be done, analyzing each item. You'll also want to do some null/value checks.

Error: No toolchains found in the NDK toolchains folder for ABI with prefix: llvm

Update project gradle version

classpath ''

Update app gradle:implementation '' implementation ''

chai test array equality doesn't work as expected

This is how to use chai to deeply test associative arrays.

I had an issue trying to assert that two associative arrays were equal. I know that these shouldn't really be used in javascript but I was writing unit tests around legacy code which returns a reference to an associative array. :-)

I did it by defining the variable as an object (not array) prior to my function call:

var myAssocArray = {};   // not []
var expectedAssocArray = {};  // not []

expectedAssocArray['myKey'] = 'something';
expectedAssocArray['differentKey'] = 'something else';

// legacy function which returns associate array reference

assert.deepEqual(myAssocArray, expectedAssocArray,'compare two associative arrays');

Index of element in NumPy array

I'm torn between these two ways of implementing an index of a NumPy array:

idx = list(classes).index(var)
idx = np.where(classes == var)

Both take the same number of characters, but the first method returns an int instead of a numpy.ndarray.

Remove all padding and margin table HTML and CSS

Try using tag body to remove all margin and padding like that you want.

<body style="margin: 0;padding: 0">
    <table border="1" width="100%" cellpadding="0" cellspacing="0" bgcolor=green>
            <td >&nbsp;</td>
            <td >&nbsp;</td>
            <td >&nbsp;</td>

Strange problem with Subversion - "File already exists" when trying to recreate a directory that USED to be in my repository

This solution merges smoothly and does not lose history:

  1. Move /working-copy/offender to a temporary location.
  2. Do an svn checkout of svn+ssh:// to /working-copy/offender.
  3. Manually move your files from the temporary location into the new checkout.
  4. Delete the temporary location.

Calling filter returns <filter object at ... >

It looks like you're using python 3.x. In python3, filter, map, zip, etc return an object which is iterable, but not a list. In other words,

filter(func,data) #python 2.x

is equivalent to:

list(filter(func,data)) #python 3.x

I think it was changed because you (often) want to do the filtering in a lazy sense -- You don't need to consume all of the memory to create a list up front, as long as the iterator returns the same thing a list would during iteration.

If you're familiar with list comprehensions and generator expressions, the above filter is now (almost) equivalent to the following in python3.x:

( x for x in data if func(x) ) 

As opposed to:

[ x for x in data if func(x) ]

in python 2.x

What is the easiest way to get the current day of the week in Android?

you can use that code for Kotlin which you will use calendar class from java into Kotlin

    val day = Calendar.getInstance().get(Calendar.DAY_OF_WEEK)

    fun dayOfWeek() {
    println("What day is it today?")
    val day = Calendar.getInstance().get(Calendar.DAY_OF_WEEK)
    println( when (day) {
      1 -> "Sunday"
      2 -> "Monday"
      3 -> "Tuesday"
      4 -> "Wednesday"
      5 -> "Thursday"
      6 -> "Friday"
      7 -> "Saturday"
      else -> "Time has stopped"

Access denied for user 'root'@'localhost' while attempting to grant privileges. How do I grant privileges?

You may have come to this question with MySQL version 8 installed (like me) and not found a satisfactory answer. You can no longer create users like this in version 8:


The rather confusing error message that you get back is: ERROR 1410 (42000): You are not allowed to create a user with GRANT

In order to create users in version 8 you have to do it in two steps:

CREATE USER 'steves'@'[hostname].com' IDENTIFIED BY '[OBSCURED]';
GRANT ALL PRIVILEGES ON *.* TO 'steves'@'[hostname].com' WITH GRANT OPTION;

Of course, if you prefer, you can also supply a limited number of privileges (instead of GRANT ALL PRIVILEGES), e.g. GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, ALTER

How to find lines containing a string in linux

Write the queue job information in long format to text file

qstat -f > queue.txt

Grep job names

grep 'Job_Name' queue.txt

html select option SELECTED

foreach ($array as $value => $name) {
     echo '<option value="' . htmlentities($value) . '"' . (($_GET['sel'] === $value) ? ' selected="selected"') . '>' . htmlentities($name) . '</option>';

This is fairly neat, and, I think, self-explanatory.

How to use AND in IF Statement

If there are no typos in the question, you got the conditions wrong:

You said this:

IF cells (i,"A") contains the text 'Miami'

...but your code says:

If Cells(i, "A") <> "Miami"

--> <> means that the value of the cell is not equal to "Miami", so you're not checking what you think you are checking.

I guess you want this instead:

If Cells(i, "A") like "*Miami*"


Sorry, but I can't really help you more. As I already said in a comment, I'm no Excel VBA expert.
Normally I would open Excel now and try your code myself, but I don't even have Excel on any of my machines at home (I use OpenOffice).

Just one general thing: can you identify the row that does not work?
Maybe this helps someone else to answer the question.

Does it ever execute (or at least try to execute) the Cells(i, "C").Value = "BA" line?
Or is the If Cells(i, "A") like "*Miami*" stuff already False?
If yes, try checking just one cell and see if that works.

How can I commit files with git?

The command for commiting all changed files:

git commit -a -m 'My commit comments'

-a = all edited files

-m = following string is a comment.

This will commit to your local drives / folders repo. If you want to push your changes to a git server / remotely hosted server, after the above command type:

git push

GitHub's cheat sheet is quite handy.

curl: (6) Could not resolve host:; Name or service not known

Try nslookup to determine if there's a DNS issue. is your local network address and it looks like your system is using it as a DNS server. Is this your gateway/modem router as well? What happens when you try ping Can you browse to it on a Internet web browser?

Integer value in TextView

TextView tv = new TextView(this);
tv.setText("" + 4);

Cannot truncate table because it is being referenced by a FOREIGN KEY constraint?

You could try DELETE FROM <your table >;.

The server will show you the name of the restriction and the table, and deleting that table you can delete what you need.

java.lang.NoSuchMethodError: org.apache.commons.codec.binary.Base64.encodeBase64String() in Java EE application

Simply create an object of Base64 and use it to encode or decode, when using org.apache.commons.codec.binary.Base64 library

To Encode

Base64 ed=new Base64();

String encoded=new String(ed.encode("Hello".getBytes()));

Replace "Hello" with the text to be encoded in String Format.

To Decode

Base64 ed=new Base64();

String decoded=new String(ed.decode(encoded.getBytes()));

Here encoded is the String variable to be decoded

Using a different font with twitter bootstrap

Hi you can create a customized build on bootstrap, just change the font name in the following pages

Bootstrap 2.3.2

Bootstrap 3

After that, make sure to use proper @font-face in a css file and link that to your page. Or you could use font kit generators.

Whitespaces in java

For a non-regular expression approach, you can check Character.isWhitespace for each character.

boolean containsWhitespace(String s) {
    for (int i = 0; i < s.length(); ++i) {
        if (Character.isWhitespace(s.charAt(i)) {
            return true;
    return false;

Which are the white spaces in Java?

The documentation specifies what Java considers to be whitespace:

public static boolean isWhitespace(char ch)

Determines if the specified character is white space according to Java. A character is a Java whitespace character if and only if it satisfies one of the following criteria:

  • It is a Unicode space character (SPACE_SEPARATOR, LINE_SEPARATOR, or PARAGRAPH_SEPARATOR) but is not also a non-breaking space ('\u00A0', '\u2007', '\u202F').
  • It is '\u0009', HORIZONTAL TABULATION.
  • It is '\u000A', LINE FEED.
  • It is '\u000B', VERTICAL TABULATION.
  • It is '\u000C', FORM FEED.
  • It is '\u000D', CARRIAGE RETURN.
  • It is '\u001C', FILE SEPARATOR.
  • It is '\u001D', GROUP SEPARATOR.
  • It is '\u001E', RECORD SEPARATOR.
  • It is '\u001F', UNIT SEPARATOR.

FromBody string parameter is giving null

After a long nightmare of fiddling with Google and trying out the wrong code in Stack Overflow I discovered changing ([FromBody] string model) to ([FromBody] object model) does wonders please not i am using .NET 4.0 yes yes i know it s old but ...

Groovy / grails how to determine a data type?

somObject instanceof Date

should be

somObject instanceOf Date

Can I get a patch-compatible output from git-diff?

Just use -p1: you will need to use -p0 in the --no-prefix case anyway, so you can just leave out the --no-prefix and use -p1:

$ git diff > save.patch
$ patch -p1 < save.patch

$ git diff --no-prefix > save.patch
$ patch -p0 < save.patch

Convert InputStream to byte array in Java

In new version,


Regex: Specify "space or start of string" and "space or end of string"

\b matches at word boundaries (without actually matching any characters), so the following should do what you want:


Check for database connection, otherwise display message

Try this:

$servername   = "localhost";
$database = "database";
$username = "user";
$password = "password";

// Create connection
$conn = new mysqli($servername, $username, $password, $database);
// Check connection
if ($conn->connect_error) {
   die("Connection failed: " . $conn->connect_error);
  echo "Connected successfully";

ASP.NET MVC get textbox input value

you can do it so simple:

First: For Example in Models you have User.cs with this implementation

public class User
   public string username { get; set; }
   public string age { get; set; }

We are passing the empty model to user – This model would be filled with user’s data when he submits the form like this

public ActionResult Add()
  var model = new User();
  return View(model);

When you return the View by empty User as model, it maps with the structure of the form that you implemented. We have this on HTML side:

@model MyApp.Models.Student
@using (Html.BeginForm()) 

    <div class="form-horizontal">
        <hr />
        @Html.ValidationSummary(true, "", new { @class = "text-danger" })
        <div class="form-group">
            @Html.LabelFor(model => model.username, htmlAttributes: new { 
                           @class = "control-label col-md-2" })
            <div class="col-md-10">
                 @Html.EditorFor(model => model.username, new { 
                                 htmlAttributes = new { @class = "form-
                                 control" } })
                 @Html.ValidationMessageFor(model => model.userame, "", 
                                            new { @class = "text-danger" })

        <div class="form-group">
            @Html.LabelFor(model => model.age, htmlAttributes: new { @class 
                           = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.age, new { htmlAttributes = 
                                new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.age, "", new { 
                                           @class = "text-danger" })
        <div class="form-group">
            <div class="col-md-offset-2 col-md-10">
                <input type="submit" value="Create" class="btn btn-default" 

So on button submit you will use it like this

public ActionResult Add(User user)
   // now user.username has the value that user entered on form

Java: Why is the Date constructor deprecated, and what do I use instead?

The Date constructor expects years in the format of years since 1900, zero-based months, one-based days, and sets hours/minutes/seconds/milliseconds to zero.

Date result = new Date(year, month, day);

So using the Calendar replacement (zero-based years, zero-based months, one-based days) for the deprecated Date constructor, we need something like:

Calendar calendar = Calendar.getInstance();
calendar.clear(); // Sets hours/minutes/seconds/milliseconds to zero
calendar.set(year + 1900, month, day);
Date result = calendar.getTime();

Or using Java 1.8 (which has zero-based year, and one-based months and days):

Date result = Date.from(LocalDate.of(year + 1900, month + 1, day).atStartOfDay(ZoneId.systemDefault()).toInstant());

Here are equal versions of Date, Calendar, and Java 1.8:

int year = 1985; // 1985
int month = 1; // January
int day = 1; // 1st

// Original, 1900-based year, zero-based month, one-based day
Date date1 = new Date(year - 1900, month - 1, day);

// Calendar, zero-based year, zero-based month, one-based day
Calendar calendar = Calendar.getInstance();
calendar.clear(); // Sets hours/minutes/seconds/milliseconds to zero
calendar.set(year, month - 1, day);
Date date2 = calendar.getTime();

// Java-time back to Date, zero-based year, one-based month, one-based day
Date date3 = Date.from(LocalDate.of(year, month, day).atStartOfDay(ZoneId.systemDefault()).toInstant());

SimpleDateFormat format = new SimpleDateFormat("yyyy-MMM-dd HH:mm:ss.SSS");

// All 3 print "1985-Jan-01 00:00:00.000"

Using Git, show all commits that are in one branch, but not the other(s)

While some of the answers posted here will help find what you seek, the following sub-command of git branch is a more suitable solution for your task.

--merged is used to find all branches which can be safely deleted, since those branches are fully contained by HEAD.

While in master one could run the command to enumerate the branches one could safely remove, like so:

git branch --merged
* master

# Delete local and remote tracking branches you don't want
git branch -d fpg_download_links
git push origin :fpg_download_links
git branch -d master_merge_static
git push origin :master_merge_static

# There is also a flag to specify remote branches in the output
git branch --remotes --merged

Tab separated values in awk

Make sure they're really tabs! In bash, you can insert a tab using C-v TAB

$ echo "LOAD_SETTLED    LOAD_INIT       2011-01-13 03:50:01" | awk -F$'\t' '{print $1}'

Initialize/reset struct to zero/null

 struct x myX;
 memset(&x, 0, sizeof(myX));

How can I catch all the exceptions that will be thrown through reading and writing a file?

It is bad practice to catch Exception -- it's just too broad, and you may miss something like a NullPointerException in your own code.

For most file operations, IOException is the root exception. Better to catch that, instead.

How do I compare a value to a backslash?

Escape the backslash:

if message.value[0] == "/" or message.value[0] == "\\":

From the documentation:

The backslash (\) character is used to escape characters that otherwise have a special meaning, such as newline, backslash itself, or the quote character.

Simple timeout in java

Nowadays you can use

try {
    String s = CompletableFuture.supplyAsync(() -> br.readLine())
                                .get(1, TimeUnit.SECONDS);
} catch (TimeoutException e) {
    System.out.println("Time out has occurred");
} catch (InterruptedException | ExecutionException e) {
    // Handle

Create HTML table using Javascript

This beautiful code here creates a table with each td having array values. Not my code, but it helped me!

var rows = 6, cols = 7;

for(var i = 0; i < rows; i++) {
  for(var j = 0; j < cols; j++) {
    $('table').find('tr').eq(i).find('td').eq(j).attr('data-row', i).attr('data-col', j);

Stretch image to fit full container width bootstrap

Check if this solves the problem:

<div class="container-fluid no-padding">
  <div class="row">
    <div class="col-md-12">
      <img src="" alt="placeholder 960" class="img-responsive" />


.no-padding {
  padding-left: 0;
  padding-right: 0;

Css class no-padding will override default bootstrap container padding.

Full example here.

@Update If you use bootstrap 4 it could be done even simpler

<div class="container-fluid px-0">
  <div class="row">
    <div class="col-md-12">
      <img src="" alt="placeholder 960" class="img-responsive" />

Updated example here.

trigger click event from angularjs directive

This is how I was able to trigger a button click when the page loads.

<li ng-repeat="a in array">
  <a class="button" id="btn" ng-click="function(a)" index="$index" on-load-clicker>

A simple directive that takes the index from the ng-repeat and uses a condition to call the first button in the index and click it when the page loads.

        .directive('onLoadClicker', function ($timeout) {
            return {
                restrict: 'A',
                scope: {
                    index: '=index'
                link: function($scope, iElm) {
                    if ($scope.index == 0) {
                        $timeout(function() {


                        }, 0);

This was the only way I was able to even trigger an auto click programmatically in the first place. angular.element(document.querySelector('#btn')).click(); Did not work from the controller so making this simple directive seems most effective if you are trying to run a click on page load and you can specify which button to click by passing in the index. I got help through this stack-overflow answer from another post reference: onLoadClicker Directive.

JPanel Padding in Java

I will suppose your JPanel contains JTextField, for the sake of the demo.

Those components provides JTextComponent#setMargin() method which seems to be what you're looking for.

If you're looking for an empty border of any size around your text, well, use EmptyBorder

Create ul and li elements in javascript.

Here is my working code :

<!DOCTYPE html>
   ul#proList{list-style-position: inside}
   li.item{list-style:none; padding:5px;}
    <div id="renderList"></div>
        var ul = document.createElement('ul');

        productList = ['Electronics Watch','House wear Items','Kids wear','Women Fashion'];


        function renderProductList(element, index, arr) {
            var li = document.createElement('li');


            li.innerHTML=li.innerHTML + element;

working jsfiddle example here

Python Tkinter clearing a frame

Returns a list of all w's children, in their stacking order from lowest (bottom) to highest (top).

for widget in frame.winfo_children():

Will destroy all the widget in your frame. No need for a second frame.

Command Line Tools not working - OS X El Capitan, Sierra, High Sierra, Mojave

For those also having issues with heroku command line tools after upgrading, I also had to do the following in my terminal:

xcode-select --install 
brew install heroku/brew/heroku
brew link --overwrite heroku

It seems the upgrade to High Sierra messed with my symlinks in addition to forcing me to reinstall xcode tools. I kept getting 'not a directory' errors:

? stat /Users/mattymc/.local/share/heroku/client/bin/heroku: not a directory  
? fork/exec /Users/mattmcinnis/.local/share/heroku/client/bin/heroku: not a directory 

Hope that saves someone an hour :)

Warning "Do not Access Superglobal $_POST Array Directly" on Netbeans 7.4 for PHP

Although a bit late, I've come across this question while searching the solution for the same problem, so I hope it can be of any help...

Found myself in the same darkness than you. Just found this article, which explains some new hints introduced in NetBeans 7.4, including this one:

The reason why it has been added is because superglobals usually are filled with user input, which shouldn't ever be blindly trusted. Instead, some kind of filtering should be done, and that's what the hint suggests. Filter the superglobal value in case it has some poisoned content.

For instance, where I had:


I've put instead:


You have the filter_input and filters doc here:

What is the string length of a GUID?

The correct thing to do here is to store it as uniqueidentifier - this is then fully indexable, etc. at the database. The next-best option would be a binary(16) column: standard GUIDs are exactly 16 bytes in length.

If you must store it as a string, the length really comes down to how you choose to encode it. As hex (AKA base-16 encoding) without hyphens it would be 32 characters (two hex digits per byte), so char(32).

However, you might want to store the hyphens. If you are short on space, but your database doesn't support blobs / guids natively, you could use Base64 encoding and remove the == padding suffix; that gives you 22 characters, so char(22). There is no need to use Unicode, and no need for variable-length - so nvarchar(max) would be a bad choice, for example.

Python:Efficient way to check if dictionary is empty or not

Just check the dictionary:

d = {'hello':'world'}
if d:
  print 'not empty'
  print 'empty'

d = {}
if d:
  print 'not empty'
  print 'empty'

'Malformed UTF-8 characters, possibly incorrectly encoded' in Laravel

In my case I had a ucfirst on the asian letters string. This was not possible and produced a non utf8 string.

Setting background images in JFrame

Try this :


import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;

public class Test {

    public static void main(String[] args) {
        JFrame f = new JFrame();
        try {
            f.setContentPane(new JLabel(new ImageIcon( File("test.jpg")))));
        } catch (IOException e) {


By the way, this will result in the content pane not being a container. If you want to add things to it you have to subclass a JPanel and override the paintComponent method.

List of All Locales and Their Short Codes?


"Language tag syntax is defined by the IETF's BCP 47. BCP stands for 'Best Current Practice', and is a persistent name for a series of RFCs whose numbers change as they are updated. The latest RFC describing language tag syntax is RFC 5646, Tags for the Identification of Languages, and it obsoletes the older RFCs 4646, 3066 and 1766.

You used to find subtags by consulting the lists of codes in various ISO standards, but now you can find all subtags in the IANA Language Subtag Registry."

AFAIK most locale-aware applications (that are written by professionals) abide by this standard. It isn't just something somebody threw together and that different people interpret differently.

I'd strongly suggest you investigate the internationalization features of your particular development language, as you'll probably end up reinventing the wheel if you don't.

C++ -- expected primary-expression before ' '


int wordLength = wordLengthFunction(string word);


int wordLength = wordLengthFunction(word);

Create iOS Home Screen Shortcuts on Chrome for iOS

The is no API for adding a shortcut to the home screen in iOS, so no third-party browser is capable of providing that functionality.

How to yum install Node.JS on Amazon Linux

I had Node.js 6.x installed and wanted to install Node.js 8.x.

Here's the commands I used (taken from Nodejs's site with a few extra steps to handle the yum cached data):

  1. sudo yum remove nodejs: Uninstall Node.js 6.x (I don't know if this was necessary or not)
  2. curl --silent --location | sudo bash -
  3. sudo yum clean all
  4. sudo yum makecache: Regenerate metadata cache (this wasn't in the docs, but yum kept trying to install Node.jx 6.x, unsuccessfully, until I issued these last two commands)
  5. sudo yum install nodejs: Install Node.js 8.x

How do I add multiple conditions to "ng-disabled"?

Actually the ng-disabled directive works with the " || " logical operator for me. The " && " evaluate only one condition.,js,output

How do I create a link to add an entry to a calendar?

The links in Dave's post are great. Just to put a few technical details about the google links into an answer here on SO:

Google Calendar Link

<a href="">Add to gCal</a>

the parameters being:

  • action=TEMPLATE (required)
  • text (url encoded name of the event)
  • dates (ISO date format, startdate/enddate - must have both start and end time - the button generator will let you leave the endtime blank, but you must have one or it won't work.)
    • to use the user's timezone: 20131208T160000/20131208T180000
    • to use global time, convert to UTC, then use 20131208T160000Z/20131208T180000Z
    • all day events, you can use 20131208/20131209 - note that the button generator gets it wrong. You must use the following date as the end date for a one day all day event, or +1 day to whatever you want the end date to be.
  • details (url encoded event description/details)
  • location (url encoded location of the event - make sure it's an address google maps can read easily)

Update Feb 2018:

Here's a new link structure that seems to support the new google version of google calendar w/o requiring API interaction:,+link+here:+,+MA+02134

New base url:

New parameters:

  • text (name of the event)
  • dates (ISO date format, startdate/enddate - must have both start and end time)
    • an event w/ start/end times: 20131208T160000/20131208T180000
    • all day events, you can use 20131208/20131209 - end date must be +1 day to whatever you want the end date to be.
  • ctz (timezone such as America/New_York - leave blank to use the user's default timezone. Highly recommended to include this in almost all situations. For example, a reminder for a video conference: if three people in different timezones clicked this link and set a reminder for their "own" Tuesday at 10:00am, this would not work out well.)
  • details (url encoded event description/details)
  • location (url encoded location of the event - make sure it's an address google maps can read easily)
  • add (comma separated list of emails - adds guests to your new event)


  • the old url structure above now redirects here
  • supports https
  • deals w/ timezones better
  • accepts + for space in addition to %20 (urlencode vs rawurlencode in php - both work)

How to compile multiple java source files in command line

or you can use the following to compile the all java source files in current directory..

javac *.java

When should I use File.separator and when File.pathSeparator? class contains four static separator variables. For better understanding, Let's understand with the help of some code

  1. separator: Platform dependent default name-separator character as String. For windows, it’s ‘\’ and for unix it’s ‘/’
  2. separatorChar: Same as separator but it’s char
  3. pathSeparator: Platform dependent variable for path-separator. For example PATH or CLASSPATH variable list of paths separated by ‘:’ in Unix systems and ‘;’ in Windows system
  4. pathSeparatorChar: Same as pathSeparator but it’s char

Note that all of these are final variables and system dependent.

Here is the java program to print these separator variables.


public class FileSeparator {

    public static void main(String[] args) {
        System.out.println("File.separator = "+File.separator);
        System.out.println("File.separatorChar = "+File.separatorChar);
        System.out.println("File.pathSeparator = "+File.pathSeparator);
        System.out.println("File.pathSeparatorChar = "+File.pathSeparatorChar);


Output of above program on Unix system:

File.separator = /
File.separatorChar = /
File.pathSeparator = :
File.pathSeparatorChar = :

Output of the program on Windows system:

File.separator = \
File.separatorChar = \
File.pathSeparator = ;
File.pathSeparatorChar = ;

To make our program platform independent, we should always use these separators to create file path or read any system variables like PATH, CLASSPATH.

Here is the code snippet showing how to use separators correctly.

//no platform independence, good for Unix systems
File fileUnsafe = new File("tmp/abc.txt");
//platform independent and safe to use across Unix and Windows
File fileSafe = new File("tmp"+File.separator+"abc.txt");

Java client certificates over HTTPS/SSL

If you are dealing with a web service call using the Axis framework, there is a much simpler answer. If all want is for your client to be able to call the SSL web service and ignore SSL certificate errors, just put this statement before you invoke any web services:

System.setProperty("axis.socketSecureFactory", "");

The usual disclaimers about this being a Very Bad Thing to do in a production environment apply.

I found this at the Axis wiki.

How to extract an assembly from the GAC?

just navigate to C:\Windows find the [assembly] folder right click and select add to archive

wait a little

vola you have an archive file containing all the assemblies in your GAC

Set Radiobuttonlist Selected from Codebehind

You could do:

radio1.SelectedIndex = 1;

But this is the most simple form and would most likely become problematic as your UI grows. Say, for instance, if a team member inserts an item in the RadioButtonList above option2 but doesn't know we use magic numbers in code-behind to select - now the app selects the wrong index!

Maybe you want to look into using FindControl in order to determine the ListItem actually required, by name, and selecting appropriately. For instance:

//omitting possible null reference checks...
var wantedOption = radio1.FindControl("option2").Selected = true;

Reducing video size with same format and reducing frame size

ffmpeg -i <input.mp4> -b:v 2048k -s 1000x600 -fs 2048k -vcodec mpeg4 -acodec copy <output.mp4>
  • -i input file

  • -b:v videobitrate of output video in kilobytes (you have to try)

  • -s dimensions of output video

  • -fs FILESIZE of output video in kilobytes

  • -vcodec videocodec (use ffmpeg -codecs to list all available codecs)

  • -acodec audio codec for output video (only copy the audiostream, don't temper)

How to turn on WCF tracing?

Instead of you manual adding the tracing enabling bit into web.config you can also try using the WCF configuration editor which comes with VS SDK to enable tracing

Copying PostgreSQL database to another server

Here is an example using pg_basebackup

I chose to go this route because it backs up the entire database cluster (users, databases, etc.).

I'm posting this as a solution on here because it details every step I had to take, feel free to add recommendations or improvements after reading other answers on here and doing some more research.

For Postgres 12 and Ubuntu 18.04 I had to do these actions:

On the server that is currently running the database:

Update pg_hba.conf, for me located at /etc/postgresql/12/main/pg_hba.conf

Add the following line (substitute with the IP address of the server you want to copy the database to).

host  replication  postgres  trust

Update postgresql.conf, for me located at /etc/postgresql/12/main/postgresql.conf. Add the following line:

listen_addresses = '*'

Restart postgres:

sudo service postgresql restart

On the host you want to copy the database cluster to:

sudo service postgresql stop

sudo su root

rm -rf /var/lib/postgresql/12/main/*


sudo -u postgres pg_basebackup -h -U postgres -D /var/lib/postgresql/12/main/

sudo service postgresql start

Big picture - stop the service, delete everything in the data directory (mine is in /var/lib/postgreql/12). The permissions on this directory are drwx------ with user and group postgres. I could only do this as root, not even with sudo -u postgres. I'm unsure why. Ensure you are doing this on the new server you want to copy the database to! You are deleting the entire database cluster.

Make sure to change the IP address from to the IP address you are copying the database from. Copy the data from the original server with pg_basebackup. Start the service.

Update pg_hba.conf and postgresql.conf to match the original server configuration - before you made any changes adding the replication line and the listen_addresses line (in my care I had to add the ability to log-in locally via md5 to pg_hba.conf).

Note there are considerations for max_wal_senders and wal_level that can be found in the documentation. I did not have to do anything with this.

List all files in one directory PHP

Check this out : readdir()

This bit of code should list all entries in a certain directory:

if ($handle = opendir('.')) {

    while (false !== ($entry = readdir($handle))) {

        if ($entry != "." && $entry != "..") {

            echo "$entry\n";


Edit: miah's solution is much more elegant than mine, you should use his solution instead.

"Gradle Version 2.10 is required." Error

Latest gradle

Download the latest from from Complete Distribution link in android studio file ->settings ->gradle the path and paste the downloaded zip folder gradle-3.3 in that folder

4.change your gradle 2.8 to gradle 3.3 in file ->settings ->gradle

5.Or you can change your gradle wrapper in the project

6.edit YourProject\gradle\wrapper\ file and edit the field distributionUrl in to


shown in android studio's gradle files

How to link an image and target a new window

<a href="" target="_blank"> //gives blank window
<img width="220" height="250" border="0" align="center"  src=""/> // show image into new window

See the code

Reference list item by index within Django template?

{{ data.0 }} should work.

Let's say you wrote data.obj django tries data.obj and data.obj(). If they don't work it tries data["obj"]. In your case data[0] can be written as {{ data.0 }}. But I recommend you to pull data[0] in the view and send it as separate variable.

Visual Studio Code always asking for git credentials

In case you are on Windows PC Then answer you are looking for!
Install Git for Windows

That's it!

IndentationError: unindent does not match any outer indentation level

Are you sure you are not mixing tabs and spaces in your indentation white space? (That will cause that error.)

Note, it is recommended that you don't use tabs in Python code. See the style guide. You should configure Notepad++ to insert spaces for tabs.

How to make a great R reproducible example

Apart of all above answers which I found very interesting, it could sometimes be very easy as it is discussed here :- HOW TO MAKE A MINIMAL REPRODUCIBLE EXAMPLE TO GET HELP WITH R

There are many ways to make a random vector Create a 100 number vector with random values in R rounded to 2 decimals or random matrix in R

mydf1<- matrix(rnorm(20),nrow=20,ncol=5)

Note that sometimes it is very difficult to share a given data because of various reasons such as dimension etc. However, all above answers are great and very important to think and use when one wants to make a reproducible data example. But note that in order to make a data as representative as the original (in case the OP cannot share the original data), it is good to add some information with the data example as (if we call the data mydf1)

# this shows the type of the data you have 
# this shows the dimension of your data

Moreover, one should know the type, length and attributes of a data which can be Data structures

#found based on the following 
typeof(mydf1), what it is.
length(mydf1), how many elements it contains.
attributes(mydf1), additional arbitrary metadata.

#If you cannot share your original data, you can str it and give an idea about the structure of your data

PHP Fatal Error Failed opening required File

If you have SELinux running, you might have to grant httpd permission to read from /home dir using:

 sudo setsebool httpd_read_user_content=1

What is log4j's default log file dumping path

To redirect your logs output to a file, you need to use the FileAppender and need to define other file details in your file. Here is a sample properties file for the same:

# Root logger option
log4j.rootLogger=INFO, file

# Direct log messages to a log file
log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

Follow this tutorial to learn more about log4j usage:

Function to return only alpha-numeric characters from string?

Rather than preg_replace, you could always use PHP's filter functions using the filter_var() function with FILTER_SANITIZE_STRING.

Gcc error: gcc: error trying to exec 'cc1': execvp: No such file or directory

It's in this package (Ubuntu 19.04):

  sudo apt install g++-6

How to replace item in array?

var index = Array.indexOf(Array value);
        if (index > -1) {
          Array.splice(index, 1);

from here you can delete a particular value from array and based on the same index you can insert value in array .

 Array.splice(index, 0, Array value);

How can I create database tables from XSD files?

I use XSLT to do that. Write up your XSD then pass your data models through a hand written XSLT that outputs SQL commands. Writing an XSLT is way faster and reusable than a custom program /script you may write.

At least thats how I do it at work, and thanks to that I got time to hang out on SO :)

Change button text from Xcode?

If you've got a button that's hooked up to an action in your code, you can change the title without an instance variable.

For example, if the button is set to this action:


You can simply do this in the method:

-(IBAction)startSomething:(id)sender {
    [sender setTitle:@"Hello" forState:UIControlStateNormal];

Or if you're wanting to toggle the name of the button, you can create a BOOL named "buttonToggled" (for example), and toggle the name this way:

-(IBAction)toggleButton:(id)sender {
    if (!buttonToggled) {
        [sender setTitle:@"Something" forState:UIControlStateNormal];
        buttonToggled = YES;
    else {
        [sender setTitle:@"Different" forState:UIControlStateNormal];
        buttonToggled = NO;

What is the difference between #import and #include in Objective-C?

In may case I had a global variable in one of my .h files that was causing the problem, and I solved it by adding extern in front of it.

How to stop/shut down an elasticsearch node?

Stopping the service and killing the daemon are indeed the correct ways to shutdown a node. However, it's not recommended to do so directly if you want to take down a node for maintenance. In fact, if you don't have replicas you will lose data.

When you directly shutdown a node, Elasticsearch will wait for 1m (default time) for it to come back online. If it doesn't, then it will start to allocate the shards from that node to other nodes wasting lots of IO.

A typical approach would be to disable shard allocation temporarily by issuing:

PUT _cluster/settings
  "persistent": {
    "cluster.routing.allocation.enable": "none"

Now, when you take down a node, ES won't try to allocate shard from that node to other nodes and you can perform you maintenance activity and then once the node is up, you can enable shard allocation again:

PUT _cluster/settings
  "persistent": {
    "cluster.routing.allocation.enable": "all"


If you don't have replicas for all your indexes, then performing this type of activity will have downtime on some of the indexes. A cleaner way in this case would be to migrate all the shards to other nodes before taking the node down:

PUT _cluster/settings
  "transient" : {
    "cluster.routing.allocation.exclude._ip" : ""

This will move all shards from to other nodes (will take time depending on the data). Once everything is done, you can kill the node, perform maintenance and get it back online. This is a slower operation and is not required if you have replicas.

(Instead of _ip, _id, _name with wildcards will work just fine.)

More information:

Other answers have explained how to kill a process.

How to convert Base64 String to javascript file object like as from file input form?

I had a very similar requirement (importing a base64 encoded image from an external xml import file. After using xml2json-light library to convert to a json object, I was able to leverage insight from cuixiping's answer above to convert the incoming b64 encoded image to a file object.

const imgName = incomingImage['FileName'];
const imgExt = imgName.split('.').pop();
let mimeType = 'image/png';
if (imgExt.toLowerCase() !== 'png') {
    mimeType = 'image/jpeg';
const imgB64 = incomingImage['_@ttribute'];
const bstr = atob(imgB64);
let n = bstr.length;
const u8arr = new Uint8Array(n);
while (n--) {
  u8arr[n] = bstr.charCodeAt(n);
const file = new File([u8arr], imgName, {type: mimeType});

My incoming json object had two properties after conversion by xml2json-light: FileName and _@ttribute (which was b64 image data contained in the body of the incoming element.) I needed to generate the mime-type based on the incoming FileName extension. Once I had all the pieces extracted/referenced from the json object, it was a simple task (using cuixiping's supplied code reference) to generate the new File object which was completely compatible with my existing classes that expected a file object generated from the browser element.

Hope this helps connects the dots for others.

What is this weird colon-member (" : ") syntax in the constructor?

This is not obscure, it's the C++ initialization list syntax

Basically, in your case, x will be initialized with _x, y with _y, z with _z.

Read next word in java

Using Scanners, you will end up spawning a lot of objects for every line. You will generate a decent amount of garbage for the GC with large files. Also, it is nearly three times slower than using split().

On the other hand, If you split by space (line.split(" ")), the code will fail if you try to read a file with a different whitespace delimiter. If split() expects you to write a regular expression, and it does matching anyway, use split("\\s") instead, that matches a "bit" more whitespace than just a space character.

P.S.: Sorry, I don't have right to comment on already given answers.

Namenode not getting started

If you kept default configurations when running hadoop the port for the namenode would be 50070. You will need to find any processes running on this port and kill them first.

  • Stop all running hadoop with : bin/

    check all processes running in port 50070

  • sudo netstat -tulpn | grep :50070 #check any processes running in port 50070, if there are any the / will appear at the RHS of the output.

  • sudo kill -9 <process_id> #kill_the_process.

  • sudo rm -r /app/hadoop/tmp #delete the temp folder

  • sudo mkdir /app/hadoop/tmp #recreate it

  • sudo chmod 777 –R /app/hadoop/tmp (777 is given for this example purpose only)

  • bin/hadoop namenode –format #format hadoop namenode

  • bin/ #start-all hadoop services

Refer this blog

how to rotate a bitmap 90 degrees

Below is the code to rotate or re size your image in android

public class bitmaptest extends Activity {
    public void onCreate(Bundle icicle) {
        LinearLayout linLayout = new LinearLayout(this);

        // load the origial BitMap (500 x 500 px)
        Bitmap bitmapOrg = BitmapFactory.decodeResource(getResources(),

        int width = bitmapOrg.width();
        int height = bitmapOrg.height();
        int newWidth = 200;
        int newHeight = 200;

        // calculate the scale - in this case = 0.4f
        float scaleWidth = ((float) newWidth) / width;
        float scaleHeight = ((float) newHeight) / height;

        // createa matrix for the manipulation
        Matrix matrix = new Matrix();
        // resize the bit map
        matrix.postScale(scaleWidth, scaleHeight);
        // rotate the Bitmap

        // recreate the new Bitmap
        Bitmap resizedBitmap = Bitmap.createBitmap(bitmapOrg, 0, 0,
                          width, height, matrix, true);

        // make a Drawable from Bitmap to allow to set the BitMap
        // to the ImageView, ImageButton or what ever
        BitmapDrawable bmd = new BitmapDrawable(resizedBitmap);

        ImageView imageView = new ImageView(this);

        // set the Drawable on the ImageView

        // center the Image

        // add ImageView to the Layout
                new LinearLayout.LayoutParams(
                      LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT

        // set LinearLayout as ContentView

You can also check this link for details :

How do I send email with JavaScript without opening the mail client?

There needs to be some type of backend framework to send the email. This can be done via PHP/ASP.NET, or with the local mail client. If you want the user to see nothing, the best way is to tap into those by an AJAX call to a separate send_email file.

Set session variable in laravel

to set session you can try this:


also to get session data you can try this:


If you want to get all session data:


Trim specific character from a string

To my knowledge, jQuery doesnt have a built in function the method your are asking about. With javascript however, you can just use replace to change the content of your string:

x.replace(/|/i, ""));

This will replace all occurences of | with nothing.

Programmatically Install Certificate into Mozilla

I had a similar issue on a client site where the client required a authority certificate to be installed automatically for 2000+ windows users.

I created the following .vbs script to import the certificate into the current logged on users firefox cert store.

The script needs to be put in the directory containing a working copy of certutil.exe (the nss version) but programatically determines the firefox profiles location.

Option Explicit

On error resume next

Const DEBUGGING              = true
const SCRIPT_VERSION        = 0.1
Const CERTUTIL_EXCUTABLE    = "certutil.exe"
Const ForReading = 1

Dim strCertDirPath, strCertutil, files, slashPosition, dotPosition, strCmd, message
Dim file, filename, filePath, fileExtension

Dim WshShell            : Set WshShell            = WScript.CreateObject("WScript.Shell")
Dim objFilesystem      : Set objFilesystem    = CreateObject("Scripting.FileSystemObject") 
Dim certificates        : Set certificates      = CreateObject("Scripting.Dictionary")
Dim objCertDir
Dim UserFirefoxDBDir
Dim UserFirefoxDir
Dim objINIFile
Dim strNextLine,Tmppath,intLineFinder, NickName

vAPPDATA = WshShell.ExpandEnvironmentStrings("%APPDATA%") 
strCertDirPath    = WshShell.CurrentDirectory
strCertutil      = strCertDirPath & "\" & CERTUTIL_EXCUTABLE
UserFirefoxDir = vAPPDATA & "\Mozilla\Firefox"
NickName = "Websense Proxy Cert"

Set objINIFile = objFilesystem.OpenTextFile( UserFireFoxDir & "\profiles.ini", ForReading)

Do Until objINIFile.AtEndOfStream
    strNextLine = objINIFile.Readline

    intLineFinder = InStr(strNextLine, "Path=")
    If intLineFinder <> 0 Then
        Tmppath = Split(strNextLine,"=")
        UserFirefoxDBDir = UserFirefoxDir & "\" & replace(Tmppath(1),"/","\")

    End If  

'output UserFirefoxDBDir

If objFilesystem.FolderExists(strCertDirPath) And objFilesystem.FileExists(strCertutil) Then
    Set objCertDir = objFilesystem.GetFolder(strCertDirPath)
    Set files = objCertDir.Files

    For each file in files
        slashPosition = InStrRev(file, "\")
        dotPosition  = InStrRev(file, ".")
        fileExtension = Mid(file, dotPosition + 1)
        filename      = Mid(file, slashPosition + 1, dotPosition - slashPosition - 1)

        If LCase(fileExtension) = "cer" Then        
            strCmd = chr(34) & strCertutil & chr(34) &" -A -a -n " & chr(34) & NickName & chr(34) & " -i " & chr(34) & file & chr(34) & " -t " & chr(34) & "TCu,TCu,TCu" & chr(34) & " -d " & chr(34) & UserFirefoxDBDir & chr(34)
        End If        
    WshShell.LogEvent EVENTLOG_WARNING, "Script: " & WScript.ScriptFullName & " - version:" & SCRIPT_VERSION & vbCrLf & vbCrLf & message
End If

function output(message)
        Wscript.echo message
    End if
End function

Set WshShell  = Nothing
Set objFilesystem = Nothing

Radio/checkbox alignment in HTML/CSS

I think I have finally solved the problem. One commonly recommended solution is to use vertical-align: middle:

<input type="radio" style="vertical-align: middle"> Label

The problem, however, is that this still produces visible misalignments even though it should theoretically work. The CSS2 specification says that:

vertical-align: middle: Align the vertical midpoint of the box with the baseline of the parent box plus half the x-height of the parent.

So it should be in the perfect centre (the x-height is the height of the character x). However, the problem seems to be caused by the fact browsers commonly add some random uneven margins to radio buttons and checkboxes. One can check, for instance in Firefox using Firebug, that the default checkbox margin in Firefox is 3px 3px 0px 5px. I'm not sure where it comes from, but the other browsers seem to have similar margins as well. So to get a perfect alignment, one needs to get rid of these margins:

<input type="radio" style="vertical-align: middle; margin: 0px;"> Label

It is still interesting to note that in the table based solution the margins are somehow eaten and everything aligns nicely.

How to jump back to NERDTree from file in tab?

ctrl-ww Could be useful when you have limited tabs open. But could get annoying when you have too many tabs open.

I type in :NERDTree again to get the focus back on NERDTree tab instantly wherever my cursor's focus is. Hope that helps

Executing a batch script on Windows shutdown

Well, its an easy way of doing some registry changes: I tried this on 2008 r2 and 2016 servers.

Things need to be done:

  1. Create a text file "regedit.txt"
  2. Paste the following code in it:
Windows Registry Editor Version 5.00 

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Group Policy\State\Machine\Scripts]

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Group Policy\State\Machine\Scripts\Shutdown] 

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Group Policy\Scripts\Shutdown]     

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Group Policy\State\Machine\Scripts\Shutdown\0]  
"DisplayName"="Local Group Policy"    
"GPOName"="Local Group Policy"    

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Group Policy\State\Machine\Scripts\Shutdown\0\0]    

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Group Policy\Scripts\Shutdown\0]
"DisplayName"="Local Group Policy"    
"GPOName"="Local Group Policy"

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Group Policy\Scripts\Shutdown\0\0]    
  1. Save this file as regedit.reg extension

  2. Run it on any command line using below command:

    regedit.exe /s regedit.reg

html5 audio player - jquery toggle click play/pause?

You can call native methods trough trigger in jQuery. Just do this:


And the same for pause: $('.play').trigger("pause");

EDIT: as F... pointed out in the comments, you can do something similar to access properties: $('.play').prop("paused");

How to use Global Variables in C#?

First examine if you really need a global variable instead using it blatantly without consideration to your software architecture.

Let's assuming it passes the test. Depending on usage, Globals can be hard to debug with race conditions and many other "bad things", it's best to approach them from an angle where you're prepared to handle such bad things. So,

  1. Wrap all such Global variables into a single static class (for manageability).
  2. Have Properties instead of fields(='variables'). This way you have some mechanisms to address any issues with concurrent writes to Globals in the future.

The basic outline for such a class would be:

public class Globals
    private static bool _expired;
    public static bool Expired 
            // Reads are usually simple
            return _expired;
            // You can add logic here for race conditions,
            // or other measurements
            _expired = value;
    // Perhaps extend this to have Read-Modify-Write static methods
    // for data integrity during concurrency? Situational.

Usage from other classes (within same namespace)

// Read
bool areWeAlive = Globals.Expired;

// Write
// past deadline
Globals.Expired = true;

T-SQL: Opposite to string concatenation - how to split string into multiple records

SELECT substring(commaSeparatedTags,0,charindex(',',commaSeparatedTags))

will give you the first tag. You can proceed similarly to get the second one and so on by combining substring and charindex one layer deeper each time. That's an immediate solution but it works only with very few tags as the query grows very quickly in size and becomes unreadable. Move on to functions then, as outlined in other, more sophisticated answers to this post.

gradient descent using python and numpy

I know this question already have been answer but I have made some update to the GD function :


def cost(theta,X,y):
     ### Evaluate half MSE (Mean square error)
     m = len(y)
     error =,theta) - y
     J = np.sum(error ** 2)/(2*m)
     return J


def GD(X,y,theta,alpha):

    cost_histo = [0]
    theta_histo = [0]

    # an arbitrary gradient, to pass the initial while() check
    delta = [np.repeat(1,len(X))]
    # Initial theta
    old_cost = cost(theta,X,y)

    while (np.max(np.abs(delta)) > 1e-6):
        error =,theta) - y
        delta =,error)/len(y)
        trial_theta = theta - alpha * delta
        trial_cost = cost(trial_theta,X,y)
        while (trial_cost >= old_cost):
            trial_theta = (theta +trial_theta)/2
            trial_cost = cost(trial_theta,X,y)
            cost_histo = cost_histo + trial_cost
            theta_histo = theta_histo +  trial_theta
        old_cost = trial_cost
        theta = trial_theta
    Intercept = theta[0] 
    Slope = theta[1]  
    return [Intercept,Slope]

res = GD(X,y,theta,alpha)

This function reduce the alpha over the iteration making the function too converge faster see Estimating linear regression with Gradient Descent (Steepest Descent) for an example in R. I apply the same logic but in Python.

How can I do division with variables in a Linux shell?

Referencing Bash Variables Requires Parameter Expansion

The default shell on most Linux distributions is Bash. In Bash, variables must use a dollar sign prefix for parameter expansion. For example:

expr $x / $y

Of course, Bash also has arithmetic operators and a special arithmetic expansion syntax, so there's no need to invoke the expr binary as a separate process. You can let the shell do all the work like this:

x=20; y=5
echo $((x / y))

How to pipe list of files returned by find command to cat to view all the files

  1. Piping to another process (Although this WON'T accomplish what you said you are trying to do):

    command1 | command2

    This will send the output of command1 as the input of command2

  2. -exec on a find (this will do what you are wanting to do -- but is specific to find)

    find . -name '*.foo' -exec cat {} \;

    (Everything between find and -exec are the find predicates you were already using. {} will substitute the particular file you found into the command (cat {} in this case); the \; is to end the -exec command.)

  3. send output of one process as command line arguments to another process

    command2 `command1`

    for example:

    cat `find . -name '*.foo' -print`

    (Note these are BACK-QUOTES not regular quotes (under the tilde ~ on my keyboard).) This will send the output of command1 into command2 as command line arguments. Note that file names containing spaces (newlines, etc) will be broken into separate arguments, though.

docker-compose up for only certain containers

You can use the run command and specify your services to run. Be careful, the run command does not expose ports to the host. You should use the flag --service-ports to do that if needed.

docker-compose run --service-ports client server database

ngOnInit not being called when Injectable class is Instantiated

I don't know about all the lifecycle hooks, but as for destruction, ngOnDestroy actually get called on Injectable when it's provider is destroyed (for example an Injectable supplied by a component).

From the docs :

Lifecycle hook that is called when a directive, pipe or service is destroyed.

Just in case anyone is interested in destruction check this question:

Using NOT operator in IF conditions

As a general statement, its good to make your if conditionals as readable as possible. For your example, using ! is ok. the problem is when things look like

if ((a.b && c.d.e) || !f)

you might want to do something like

bool isOk = a.b;
bool isStillOk = c.d.e
bool alternateOk = !f

then your if statement is simplified to

if ( (isOk && isStillOk) || alternateOk)

It just makes the code more readable. And if you have to debug, you can debug the isOk set of vars instead of having to dig through the variables in scope. It is also helpful for dealing with NPEs -- breaking code out into simpler chunks is always good.

For loop in Objective-C

The traditional for loop in Objective-C is inherited from standard C and takes the following form:

for (/* Instantiate local variables*/ ; /* Condition to keep looping. */ ; /* End of loop expressions */)
    // Do something.

For example, to print the numbers from 1 to 10, you could use the for loop:

for (int i = 1; i <= 10; i++)
    NSLog(@"%d", i);

On the other hand, the for in loop was introduced in Objective-C 2.0, and is used to loop through objects in a collection, such as an NSArray instance. For example, to loop through a collection of NSString objects in an NSArray and print them all out, you could use the following format.

for (NSString* currentString in myArrayOfStrings)
    NSLog(@"%@", currentString);

This is logically equivilant to the following traditional for loop:

for (int i = 0; i < [myArrayOfStrings count]; i++)
    NSLog(@"%@", [myArrayOfStrings objectAtIndex:i]);

The advantage of using the for in loop is firstly that it's a lot cleaner code to look at. Secondly, the Objective-C compiler can optimize the for in loop so as the code runs faster than doing the same thing with a traditional for loop.

Hope this helps.

What are metaclasses in Python?

A metaclass is a class that tells how (some) other class should be created.

This is a case where I saw metaclass as a solution to my problem: I had a really complicated problem, that probably could have been solved differently, but I chose to solve it using a metaclass. Because of the complexity, it is one of the few modules I have written where the comments in the module surpass the amount of code that has been written. Here it is...

#!/usr/bin/env python

# Copyright (C) 2013-2014 Craig Phillips.  All rights reserved.

# This requires some explaining.  The point of this metaclass excercise is to
# create a static abstract class that is in one way or another, dormant until
# queried.  I experimented with creating a singlton on import, but that did
# not quite behave how I wanted it to.  See now here, we are creating a class
# called GsyncOptions, that on import, will do nothing except state that its
# class creator is GsyncOptionsType.  This means, docopt doesn't parse any
# of the help document, nor does it start processing command line options.
# So importing this module becomes really efficient.  The complicated bit
# comes from requiring the GsyncOptions class to be static.  By that, I mean
# any property on it, may or may not exist, since they are not statically
# defined; so I can't simply just define the class with a whole bunch of
# properties that are @property @staticmethods.
# So here's how it works:
# Executing 'from libgsync.options import GsyncOptions' does nothing more
# than load up this module, define the Type and the Class and import them
# into the callers namespace.  Simple.
# Invoking 'GsyncOptions.debug' for the first time, or any other property
# causes the __metaclass__ __getattr__ method to be called, since the class
# is not instantiated as a class instance yet.  The __getattr__ method on
# the type then initialises the class (GsyncOptions) via the __initialiseClass
# method.  This is the first and only time the class will actually have its
# dictionary statically populated.  The docopt module is invoked to parse the
# usage document and generate command line options from it.  These are then
# paired with their defaults and what's in sys.argv.  After all that, we
# setup some dynamic properties that could not be defined by their name in
# the usage, before everything is then transplanted onto the actual class
# object (or static class GsyncOptions).
# Another piece of magic, is to allow command line options to be set in
# in their native form and be translated into argparse style properties.
# Finally, the GsyncListOptions class is actually where the options are
# stored.  This only acts as a mechanism for storing options as lists, to
# allow aggregation of duplicate options or options that can be specified
# multiple times.  The __getattr__ call hides this by default, returning the
# last item in a property's list.  However, if the entire list is required,
# calling the 'list()' method on the GsyncOptions class, returns a reference
# to the GsyncListOptions class, which contains all of the same properties
# but as lists and without the duplication of having them as both lists and
# static singlton values.
# So this actually means that GsyncOptions is actually a static proxy class...
# ...And all this is neatly hidden within a closure for safe keeping.
def GetGsyncOptionsType():
    class GsyncListOptions(object):
        __initialised = False

    class GsyncOptionsType(type):
        def __initialiseClass(cls):
            if GsyncListOptions._GsyncListOptions__initialised: return

            from docopt import docopt
            from libgsync.options import doc
            from libgsync import __version__

            options = docopt(
                doc.__doc__ % __version__,
                version = __version__,
                options_first = True

            paths = options.pop('<path>', None)
            setattr(cls, "destination_path", paths.pop() if paths else None)
            setattr(cls, "source_paths", paths)
            setattr(cls, "options", options)

            for k, v in options.iteritems():
                setattr(cls, k, v)

            GsyncListOptions._GsyncListOptions__initialised = True

        def list(cls):
            return GsyncListOptions

        def __getattr__(cls, name):
            return getattr(GsyncListOptions, name)[-1]

        def __setattr__(cls, name, value):
            # Substitut option names: --an-option-name for an_option_name
            import re
            name = re.sub(r'^__', "", re.sub(r'-', "_", name))
            listvalue = []

            # Ensure value is converted to a list type for GsyncListOptions
            if isinstance(value, list):
                if value:
                    listvalue = [] + value
                    listvalue = [ None ]
                listvalue = [ value ]

            type.__setattr__(GsyncListOptions, name, listvalue)

    # Cleanup this module to prevent tinkering.
    import sys
    module = sys.modules[__name__]
    del module.__dict__['GetGsyncOptionsType']

    return GsyncOptionsType

# Our singlton abstract proxy class.
class GsyncOptions(object):
    __metaclass__ = GetGsyncOptionsType()

Difference between HashSet and HashMap?

Differences: with respect to heirarchy: HashSet implements Set. HashMap implements Map and stores a mapping of keys and values.

A use of HashSet and HashMap with respect to database would help you understand the significance of each.
HashSet: is generally used for storing unique collection objects. E.g: It might be used as implementation class for storing many-to-one relation ship between
class Item and Class Bid where (Item has many Bids) HashMap: is used to map a key to value.the value may be null or any Object /list of Object (which is object in itself).

How to extend an existing JavaScript array with another array, without creating a new array

This solution works for me (using the spread operator of ECMAScript 6):

let array = ['my', 'solution', 'works'];_x000D_
let newArray = [];_x000D_
let newArray2 = [];_x000D_
newArray.push(...array); // Adding to same array_x000D_
newArray2.push([...array]); // Adding as child/leaf/sub-array_x000D_

How to hide iOS status bar

To answer the Susitha's question: use setNeedsStatusBarAppearanceUpdate. This will make a call to prefersStatusBarHidden to refresh with your desired status bar state. Try this:

    @property (nonatomic, getter=isHideStatusBar) BOOL hideStatusBar; // Give this a default value early

    - (BOOL)prefersStatusBarHidden {
        return self.isHideStatusBar;

    - (void)someMethod {
    // triggered by an event or user action
    [self setHideStatusBar:YES];
    [self setNeedsStatusBarAppearanceUpdate];

If you want to see the status bar again, set your property hideStatusBar (or whatever you call it) to NO. Call preferStatusBarHidden indirectly by making another call to

[self setNeedsStatusBarAppearanceUpdate]

Assign command output to variable in batch file

Okay here some more complex sample for the use of For /F

:: Main
@prompt -$G
    call :REGQUERY  "Software\Classes\CLSID\{3E6AE265-3382-A429-56D1-BB2B4D1D}"

@goto :EOF

:: for the key and lists its content

    @call :EXEC "REG QUERY  HKCU\%~1"
    @call :EXEC "REG QUERY "HKLM\%~1""

@goto :EOF    

    @set output=

    @for /F "delims=" %%i in ('%~1 2^>nul') do @(
        set output=%%i

    @if not "%output%"=="" (
        echo %1 -^> %output%

@goto :EOF

I packed it into the sub function :EXEC so all of its nasty details of implementation doesn't litters the main script. So it got some kinda some batch tutorial. Notes 'bout the code:

  1. the output from the command executed via call :EXEC command is stored in %output%. Batch cmd doesn't cares about scopes so %output% will be also available in the main script.
  2. the @ the beginning is just decoration and there to suppress echoing the command line. You may delete them all and just put some @echo off at the first line is really dislike that. However like this I find debugging much more nice. Decoration Number two is prompt -$G. It's there to make command prompt look like this ->
  3. I use :: instead of rem
  4. the tilde(~) in %~1 is to remove quotes from the first argument
  5. 2^>nul is there to suppress/discard stderr error output. Normally you would do it via 2>nul. Well the ^ the batch escape char is there avoids to early resolving the redirector(>). There's some simulare use a little later in the script: echo %1 -^>... so there ^ makes it possible the output a '>' via echo what else wouldn't have been possible.
  6. even if the compare at @if not "%output%"==""looks like in most common programming languages - it's maybe different that you expected (if you're not used to MS-batch). Well remove the '@' at the beginning. Study the output. Change it tonot %output%==""-rerun and consider why this doesn't work. ;)

How to scroll to top of long ScrollView layout?

Very easy

    ScrollView scroll = (ScrollView) findViewById(;

Calling a JavaScript function named in a variable

If it´s in the global scope it´s better to use:

function foo()

var a = 'foo';

than eval(). Because eval() is evaaaaaal.

Exactly like Nosredna said 40 seconds before me that is >.<

How to get a list column names and datatypes of a table in PostgreSQL?

Updated Pratik answer to support more schemas and nullables:

    "pg_attribute".attname                                                    as "Column",
    pg_catalog.format_type("pg_attribute".atttypid, "pg_attribute".atttypmod) as "Datatype",

    not("pg_attribute".attnotnull) AS "Nullable"
    pg_catalog.pg_attribute "pg_attribute"
    "pg_attribute".attnum > 0
    AND NOT "pg_attribute".attisdropped
    AND "pg_attribute".attrelid = (
        SELECT "pg_class".oid
        FROM pg_catalog.pg_class "pg_class"
            LEFT JOIN pg_catalog.pg_namespace "pg_namespace" ON "pg_namespace".oid = "pg_class".relnamespace
            "pg_namespace".nspname = 'schema'
            AND "pg_class".relname = 'table'

Where are environment variables stored in the Windows Registry?

I always had problems with that, and I made a getx.bat script:

:: getx %envvar% [\m]
:: Reads envvar from user environment variable and stores it in the getxvalue variable
:: with \m read system environment

@SETLOCAL EnableDelayedExpansion
@echo OFF

@set l_regpath="HKEY_CURRENT_USER\Environment"
@if "\m"=="%2" set l_regpath="HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment"

::REG ADD "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment" /v PATH /t REG_SZ /f /d "%PATH%"
::@REG QUERY %l_regpath% /v %1 /S

@FOR /F "tokens=*" %%A IN ('REG QUERY %l_regpath% /v %1 /S') DO (
@  set l_a=%%A
@    if NOT "!l_a!"=="!l_a:    =!" set l_line=!l_a!

:: Delimiter is four spaces. Change it to tab \t
@set l_line=!l_line!
@set l_line=%l_line:    =    %

@set getxvalue=

@FOR /F "tokens=3* delims=  " %%A IN ("%l_line%") DO (
@    set getxvalue=%%A
@set getxvalue=!getxvalue!
@echo %getxvalue% > getxfile.tmp.txt

:: We already used tab as a delimiter
@FOR /F "delims=    " %%A IN (getxfile.tmp.txt) DO (
    @set getxvalue=%%A
@del getxfile.tmp.txt

@echo ON

Handlebars/Mustache - Is there a built in way to loop through the properties of an object?

EDIT: Handlebars now has a built-in way of accomplishing this; see the selected answer above. When working with plain Mustache, the below still applies.

Mustache can iterate over items in an array. So I'd suggest creating a separate data object formatted in a way Mustache can work with:

var o = {
  bob : 'For sure',
  roger: 'Unknown',
  donkey: 'What an ass'
mustacheFormattedData = { 'people' : [] };

for (var prop in o){
  if (o.hasOwnProperty(prop)){
      'key' : prop,
      'value' : o[prop]

Now, your Mustache template would be something like:

  {{key}} : {{value}}

Check out the "Non-Empty Lists" section here:

What good are SQL Server schemas?

They can also provide a kind of naming collision protection for plugin data. For example, the new Change Data Capture feature in SQL Server 2008 puts the tables it uses in a separate cdc schema. This way, they don't have to worry about a naming conflict between a CDC table and a real table used in the database, and for that matter can deliberately shadow the names of the real tables.

RedirectToAction with parameter

I had this issue as well, and quite a nice way to do it if you are within the same controller is to use named parameters:

return RedirectToAction(actionName: "Action", routeValues: new { id = 99 });

How to display request headers with command line curl

the -v option for curl is too verbose in the error output which contains the leading *(status line) or >(request head field) or <(response head field). to get only the request head field:

curl -v -sS 2>&1 >/dev/null | grep '>' | cut -c1-2 --complement

to get only the request head field:

curl -v -sS 2>&1 >/dev/null | grep '<' | cut -c1-2 --complement

or to dump it into /tmp/test.txt file with the -D option

curl -D /tmp/test.txt -sS > /dev/null

in order to filter the -v output, you should direct the error output to terminal and the std output to /dev/null, the -s option is to forbid the progress metering

Convert character to ASCII numeric value in java

Or you can use Stream API for 1 character or a String starting in Java 1.8:

public class ASCIIConversion {
    public static void main(String[] args) {
        String text = "adskjfhqewrilfgherqifvehwqfjklsdbnf";


Joins in update statements are non-standard and not supported by all vendors. What you're trying to do can be accomplished with a sub-select:

  firstfield = (select 'stuff' concat something from file2 where substr(file1.field1, 10, 20) = substr(,1,10) )
where like 'BLAH%'

How to read an http input stream

Try with this code:

InputStream in = address.openStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(in));
StringBuilder result = new StringBuilder();
String line;
while((line = reader.readLine()) != null) {
System.out.println(result.toString()); invalid stream header: 54657374

Clearly you aren't sending the data with ObjectOutputStream: you are just writing the bytes.

  • If you read with readObject() you must write with writeObject().
  • If you read with readUTF() you must write with writeUTF().
  • If you read with readXXX() you must write with writeXXX(), for most values of XXX.