How to export a variable from a module in JavaScript?

Question

According to this post we know that variables can be exported from one module in JavaScript:

// module.js
(function(handler) {
  var MSG = {};

  handler.init = init;
  handler.MSG = MSG;

  function init() {
    // do initialization on MSG here
    MSG = ...
  }
})(module.exports);

// app.js
require('controller');
require('module').init();

// controller.js
net = require('module');

console.log(net.MSG); // output: empty object {}

Those above codes are in Node.js and I get one empty object in my controller.js. Could you please help me figure out the reason of this?

Update1

I have updated the above codes:

// module.js
(function(handler) {
  // MSG is local global variable, it can be used other functions
  var MSG = {};

  handler.init = init;
  handler.MSG = MSG;

  function init(config) {
    // do initialization on MSG through config here
    MSG = new NEWOBJ(config);
    console.log('init is invoking...');
  }
})(module.exports);

// app.js
require('./module').init();
require('./controller');

// controller.js
net = require('./module');
net.init();
console.log(net.MSG); // output: still empty object {}

Output: still empty object. Why?

You are overwriting the local variable, not the handler property. If you must, do assign to hander.MSG, but it would be better to just extend the existing object. — Bergi
– Bergi, Commented May 7, 2015 at 4:12

Scimonster · Accepted Answer · 2015-05-06 09:38:51Z

1

When you console.log(net.MSG) in controller.js, you have not yet called init(). That only comes later in app.js.

If you init() in controller.js it should work.

Another issue i discovered through testing.

When you do MSG = {t: 12}; in init(), you overwrite MSG with a new object, but that doesn't affect handler.MSG's reference. You need to either set handler.MSG directly, or modify MSG: MSG.t = 12;.

edited May 6, 2015 at 9:38

answered May 6, 2015 at 9:14

Scimonster

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1 Comment

Scimonster Over a year ago

I found another reason. Edited.

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