Share variables between files in Node js

Question

Here are 2 files      main js require    modules    console log name      prints  foobar      module js name    foobar     When I don t have  var  it works  But when I have      module js var name    foobar     name will be undefined in main js   I have heard that global variables are bad and you better use  var  before the references  But is this a case where global variables are good

User · Answer

If we need to share multiple variables use the below format

//module.js
   let name='foobar';
   let city='xyz';
   let company='companyName';

   module.exports={
    name,
    city,
    company
  }

Usage

  // main.js
    require('./modules');
    console.log(name); // print 'foobar'

User · Answer

Save any variable that want to be shared as one object  Then pass it to loaded module so it could access the variable through object reference       main js var myModule   require    module js    var shares    value 123       Initialize module and pass the shareable object myModule init shares       The value was changed from init2 on the other file console log shares value      789   On the other file       module js var shared   null   function init2        console log shared value      123     shared value   789     module exports         init function obj              Save the shared object on current module         shared   obj              Call something outside         init2

User · Answer

With a different opinion  I think the global variables might be the best choice if you are going to publish your code to npm  cuz you cannot be sure that all packages are using the same release of your code  So if you use a file for exporting a singleton object  it will cause issues here  You can choose global  require main or any other objects which are shared across files  Otherwise  install your package as an optional dependency package can avoid this problem  Please tell me if there are some better solutions

User · Answer

a variable declared with or without the var keyword got attached to the global object  This is the basis for creating global variables in Node by declaring variables without the var keyword  While variables declared with the var keyword remain local to a module   see this article for further understanding - https   www hacksparrow com global-variables-in-node-js html

User · Answer

I m unable to find an scenario where a global var is the best option  of course you can have one  but take a look at these examples and you may find a better way to accomplish the same   Scenario 1  Put the stuff in config files  You need some value that it s the same across the application  but it changes depending on the environment  production  dev or test   the mailer type as example  you d need      File  config environments production json        mailerType    SMTP        mailerConfig            service    Gmail                  and     File  config environments test json        mailerType    Stub        mailerConfig            error   false            make a similar config for dev too   To decide which config will be loaded make a main config file  this will be used all over the application      File  config config js var     require  underscore     module exports     extend      require   dirname        config environments     process env NODE ENV     json             And now you can get the data like this      File  server js     var config   require    config config        mailer setTransport nodemailer createTransport config mailerType  config mailerConfig      Scenario 2  Use a constants file     File  constants js module exports       appName   My neat app     currentAPIVersion  3      And use it this way     File  config routes js  var constants   require     constants     module exports   function app  passport  auth      var apiroot     api v    constants currentAPIVersion        app post apiroot     users   users create         Scenario 3  Use a helper function to get set the data  Not a big fan of this one  but at least you can track the use of the  name   citing the OP s example  and put validations in place      File  helpers nameHelper js  var  name    I shall not be null   exports getName   function       return  name      exports setName   function name        validate the name       name   name       And use it     File  controllers users js  var nameHelper   require     helpers nameHelper js     exports create   function req  res  next      var user   new User      user name   req body name    nameHelper getName            There could be a use case when there is no other solution than having a global var  but usually you can share the data in your app using one of these scenarios  if you are starting to use node js  as I was sometime ago  try to organize the way you handle the data over there because it can get messy really quick

User · Answer

Global variables are almost never a good thing  maybe an exception or two out there      In this case  it looks like you really just want to export your  name  variable   E g       module js var name    foobar      export it exports name   name    Then  in main js       main js    get a reference to your required module var myModule   require    module        name is a member of myModule due to the export above var name   myModule name

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