Share variables between files in Node.js?

user_224922 0
Viewed 277622

Here are 2 files:

// main.js
require('./module');
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?

node.js global-variables javascript
8 Answers

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_20117410

Not a new approach but a bit optimized. Create a file with global variables and share them by export and require. In this example, Getter and Setter are more dynamic and global variables can be readonly. To define more globals, just add them to globals object.

global.js

const globals = {
  myGlobal: {
    value: 'can be anytype: String, Array, Object, ...'
  },
  aReadonlyGlobal: {
    value: 'this value is readonly',
    protected: true
  },
  dbConnection: {
    value: 'mongoClient.db("database")'
  },
  myHelperFunction: {
    value: function() { console.log('do help') }
  },
}

exports.get = function(global) {
  // return variable or false if not exists
  return globals[global] && globals[global].value ? globals[global].value : false;
};

exports.set = function(global, value) {
  // exists and is protected: return false
  if (globals[global] && globals[global].protected && globals[global].protected === true)
    return false;
  // set global and return true
  globals[global] = { value: value };
  return true;
};

examples to get and set in any-other-file.js

const globals = require('./globals');

console.log(globals.get('myGlobal'));
// output: can be anytype: String, Array, Object, ...

globals.get('myHelperFunction')();
// output: do help

let myHelperFunction = globals.get('myHelperFunction');
myHelperFunction();
// output: do help

console.log(globals.set('myGlobal', 'my new value'));
// output: true
console.log(globals.get('myGlobal'));
// output: my new value

console.log(globals.set('aReadonlyGlobal', 'this shall not work'));
// output: false
console.log(globals.get('aReadonlyGlobal'));
// output: this value is readonly

console.log(globals.get('notExistingGlobal'));
// output: false
user_109442190

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_13234610

If the target is the browser (by bundling Node code via Parcel.js or similar), you can simply set properties on the window object, and they become global variables:

window.variableToMakeGlobal = value;

Then you can access this variable from all modules (and more generally, from any Javascript context).

user_39509820
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