[angular] access key and value of object using *ngFor

I am a bit confused about how to get the key and value of an object in angular2 while using *ngFor for iterating over the object. I know in angular 1.x there is a syntax like

ng-repeat="(key, value) in demo"

but I don't know how to do the same in angular2. I have tried something similar, without success:

    <ul>
      <li *ngFor='#key of demo'>{{key}}</li>
    </ul>

    demo = {
        'key1': [{'key11':'value11'}, {'key12':'value12'}],
        'key2': [{'key21':'value21'}, {'key22':'value22'}],
      }

Here is a plnkr with my attempt: http://plnkr.co/edit/mIj619FncOpfdwrR0KeG?p=preview

How can I get key1 and key2 dynamically using *ngFor? After searching extensively, I found the idea of using pipes but I don't know how to go about it. Is there any inbuilt pipe for doing the same in angular2?

You could create a custom pipe to return the list of key for each element. Something like that:

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

@Pipe({name: 'keys'})
export class KeysPipe implements PipeTransform {
  transform(value, args:string[]) : any {
    let keys = [];
    for (let key in value) {
      keys.push(key);
    }
    return keys;
  }
}

and use it like that:

<tr *ngFor="let c of content">           
  <td *ngFor="let key of c | keys">{{key}}: {{c[key]}}</td>
</tr>

Edit

You could also return an entry containing both key and value:

@Pipe({name: 'keys'})
export class KeysPipe implements PipeTransform {
  transform(value, args:string[]) : any {
    let keys = [];
    for (let key in value) {
      keys.push({key: key, value: value[key]});
    }
    return keys;
  }
}

and use it like that:

<span *ngFor="let entry of content | keys">           
  Key: {{entry.key}}, value: {{entry.value}}
</span>

There's a real nice library that does this among other nice pipes. It's called ngx-pipes.

For example, keys pipe returns keys for an object, and values pipe returns values for an object:

keys pipe

<div *ngFor="let key of {foo: 1, bar: 2} | keys">{{key}}</div> 
<!-- Output: 'foo' and 'bar -->

values pipe

<div *ngFor="let value of {foo: 1, bar: 2} | values">{{value}}</div>
<!-- Output: 1 and 2 -->

No need to create your own custom pipe :)

From Angular 6.1 you can use the keyvalue pipe:

<div *ngFor="let item of testObject | keyvalue">
    Key: <b>{{item.key}}</b> and Value: <b>{{item.value}}</b>
</div>

But it has the inconvenient that sorts the resulting list by the key value. If you need something neutral:

@Pipe({ name: 'keyValueUnsorted', pure: false  })
export class KeyValuePipe implements PipeTransform {
  transform(input: any): any {
    let keys = [];
    for (let key in input) {
      if (input.hasOwnProperty(key)) {
        keys.push({ key: key, value: input[key]});
      }
    }
    return keys;
  }
}

Don't forget to specify the pure:false pipe attribute. In this case, the pipe is invoked on each change-detection cycle, even if the input reference has not changed (so is the case when you add properties to an object).

Elaboration of @Thierry's answer with example.

There is no inbuilt pipe or method to get key and value from the *ngFor loop. so we have to create custom pipe for the same. as thierry said here is the answer with code.

** The pipe class implements the PipeTransform interface's transform method that takes an input value and an optional array of parameter strings and returns the transformed value.

** The transform method is essential to a pipe. The PipeTransform interface defines that method and guides both tooling and the compiler. It is optional; Angular looks for and executes the transform method regardless. for more info regards pipe refer here

import {Component, Pipe, PipeTransform} from 'angular2/core';
import {CORE_DIRECTIVES, NgClass, FORM_DIRECTIVES, Control, ControlGroup, FormBuilder, Validators} from 'angular2/common';

@Component({
    selector: 'my-app',
    templateUrl: 'mytemplate.html',
    directives: [CORE_DIRECTIVES, FORM_DIRECTIVES],
    pipes: [KeysPipe]
})
export class AppComponent { 

  demo = {
    'key1': 'ANGULAR 2',
    'key2': 'Pardeep',
    'key3': 'Jain',
  }
}


@Pipe({name: 'keys'})
export class KeysPipe implements PipeTransform {
  transform(value, args:string[]) : any {
    let keys = [];
    for (let key in value) {
      keys.push({key: key, value: value[key]});
    }
    return keys;
  }
}

and HTML part is:

<ul>
  <li *ngFor='#key of demo | keys'>
   Key: {{key.key}}, value: {{key.value}}
  </li>
</ul>

Working Plnkr http://plnkr.co/edit/50LlK0k6OnMnkc2kNHM2?p=preview

update to RC

as suggested by user6123723(thanks) in comment here is update.

<ul>
  <li *ngFor='let key of demo | keys'>
   Key: {{key.key}}, value: {{key.value}}
  </li>
</ul>

Have Object.keys accessible in the template and use it in *ngFor.

@Component({
  selector: 'app-myview',
  template: `<div *ngFor="let key of objectKeys(items)">{{key + ' : ' + items[key]}}</div>`
})

export class MyComponent {
  objectKeys = Object.keys;
  items = { keyOne: 'value 1', keyTwo: 'value 2', keyThree: 'value 3' };
  constructor(){}
}

Thanks for the pipe but i had to make some changes before i could use it in angular 2 RC5. Changed the Pipe import line and also added type of any to the keys array initialization.

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

 @Pipe({name: 'keys'})
 export class KeysPipe implements PipeTransform {
 transform(value) {
   let keys:any = [];
   for (let key in value) {
      keys.push( {key: key, value: value[key]} );
    }
     return keys;
  }
}

Here is the simple solution

You can use typescript iterators for this

import {Component} from 'angular2/core';
declare var Symbol;
@Component({
    selector: 'my-app',
    template:`<div>
    <h4>Iterating an Object using Typescript Symbol</h4><br>
Object is : <p>{{obj | json}}</p>
</div>
============================<br>
Iterated object params are:
<div *ngFor="#o of obj">
{{o}}
</div>

`
})
export class AppComponent {
  public obj: any = {
    "type1": ["A1", "A2", "A3","A4"],
    "type2": ["B1"],
    "type3": ["C1"],
    "type4": ["D1","D2"]
  };

  constructor() {
    this.obj[Symbol.iterator] =  () => {
          let i =0;

          return {
            next: () => {
              i++;
              return {
                  done: i > 4?true:false,
                  value: this.obj['type'+i]
              }
            }
          }
    };
  }
}

http://plnkr.co/edit/GpmX8g?p=info

I think Object.keys is the best solution to this problem. For anyone that comes across this answer and is trying to find out why Object.keys is giving them ['0', '1'] instead of ['key1', 'key2'], a cautionary tale - beware the difference between "of" and "in":

I was already using Object.keys, something similar to this:

interface demo {
    key: string;
    value: string;
}

createDemo(mydemo: any): Array<demo> {
    const tempdemo: Array<demo> = [];

    // Caution: use "of" and not "in"
    for (const key of Object.keys(mydemo)) {
        tempdemo.push(
            { key: key, value: mydemo[key]}
        );
    }

    return tempdemo;
}

However, instead of

for (const key OF Object.keys(mydemo)) {

I had inadvertently wrote

for (const key IN Object.keys(mydemo)) {

which "worked" perfectly fine without any error and returned

[{key: '0', value: undefined}, {key: '1', value: undefined}]

That cost me about 2 hours googling and cursing..

(slaps forehead)

None of the answers here worked for me out of the box, here is what worked for me:

Create pipes/keys.ts with contents:

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

@Pipe({name: 'keys'})
export class KeysPipe implements PipeTransform
{
    transform(value:any, args:string[]): any {
        let keys:any[] = [];
        for (let key in value) {
            keys.push({key: key, value: value[key]});
        }
        return keys;
    }
}

Add to app.module.ts (Your main module):

import { KeysPipe } from './pipes/keys';

and then add to your module declarations array something like this:

@NgModule({
    declarations: [
        KeysPipe
    ]
})
export class AppModule {}

Then in your view template you can use something like this:

<option *ngFor="let entry of (myData | keys)" value="{{ entry.key }}">{{ entry.value }}</option>

Here is a good reference I found if you want to read more.

change demo type to array or iterate over your object and push to another array

public details =[];   
Object.keys(demo).forEach(key => {
      this.details.push({"key":key,"value":demo[key]);
    });

and from html:

<div *ngFor="obj of details">
  <p>{{obj.key}}</p>
  <p>{{obj.value}}</p>
  <p></p>
</div>

Thought of adding an answer for Angular 8:

For looping you can do:

<ng-container *ngFor="let item of BATCH_FILE_HEADERS | keyvalue: keepOriginalOrder">
   <th nxHeaderCell>{{'upload.bulk.headings.'+item.key |translate}}</th>
</ng-container>

Also if you need the above array to keep the original order then declare this inside your class:

public keepOriginalOrder = (a, b) => a.key;

@Marton had an important objection to the accepted answer on the grounds that the pipe creates a new collection on each change detection. I would instead create an HtmlService which provides a range of utility functions which the view can use as follows:

@Component({
  selector: 'app-myview',
  template: `<div *ngFor="let i of html.keys(items)">{{i + ' : ' + items[i]}}</div>`
})
export class MyComponent {
  items = {keyOne: 'value 1', keyTwo: 'value 2', keyThree: 'value 3'};
  constructor(private html: HtmlService){}
}

@Injectable()
export class HtmlService {
  keys(object: {}) {
    return Object.keys(object);
  }
  // ... other useful methods not available inside html, like isObject(), isArray(), findInArray(), and others...
}

you can get dynamic object's key with by trying this

myObj['key']

You have to do it like this for now, i know not very efficient as you don't want to convert the object you receive from firebase.

    this.af.database.list('/data/' + this.base64Email).subscribe(years => {
        years.forEach(year => {

            var localYears = [];

            Object.keys(year).forEach(month => {
                localYears.push(year[month])
            });

            year.months = localYears;

        })

        this.years = years;

    });

Update

In 6.1.0-beta.1 KeyValuePipe was introduced https://github.com/angular/angular/pull/24319

<div *ngFor="let item of {'b': 1, 'a': 1} | keyvalue">
  {{ item.key }} - {{ item.value }}
</div>

Plunker Example

Previous version

Another approach is to create NgForIn directive that will be used like:

<div *ngFor="let key in obj">
   <b>{{ key }}</b>: {{ obj[key] }}
</div>

Plunker Example

ngforin.directive.ts

@Directive({
  selector: '[ngFor][ngForIn]'
})
export class NgForIn<T> extends NgForOf<T> implements OnChanges {

  @Input() ngForIn: any;

  ngOnChanges(changes: NgForInChanges): void {
    if (changes.ngForIn) {
      this.ngForOf = Object.keys(this.ngForIn) as Array<any>;

      const change = changes.ngForIn;
      const currentValue = Object.keys(change.currentValue);
      const previousValue = change.previousValue ? Object.keys(change.previousValue) : undefined;
      changes.ngForOf =  new SimpleChange(previousValue, currentValue, change.firstChange);

      super.ngOnChanges(changes);
    }
  }
}

Use index:

<div *ngFor="let value of Objects; index as key">

Usage:

{{key}} -> {{value}}

If you're already using Lodash, you can do this simple approach which includes both key and value:

<ul>
  <li *ngFor='let key of _.keys(demo)'>{{key}}: {{demo[key]}}</li>
</ul>

In the typescript file, include:

import * as _ from 'lodash';

and in the exported component, include:

_: any = _;