Discussion on: What the heck are CJS, AMD, UMD, and ESM in Javascript?

[Eugene Karataev]

Can you please clarify?

When CJS imports, it will give you a copy of the imported object.

Let's say we have three files:

// obj.js
module.exports = {
  a: 42
};

// bar.js
const fooObj = require('./obj');

console.log('obj from bar', fooObj);

// index.js
const obj = require('./obj');

obj.a = 50;
console.log('obj', obj);

require('./bar');

Console output after run node index.js:

obj { a: 50 }
obj from bar { a: 50 }

It's clear that index.js and bar.js share the same object from obj.js.

[almaember]

Not like you should be changing modules anyways...

[Sam]

Because obj.js is exporting an object literal. The first time you require obj.js the object is instantiated, and assigned memory allocation. Every time you require it, it's the same object, from memory. If obj.js was exporting a function that returned an abject, well that would be different.

[Eugene Karataev]

If obj.js was exporting a function that returned an abject, well that would be different.

Agree. But in this case the exported function will be the same for all modules (i.e. the function will not be copied for every import).

[Sam]

Right