What is the purpose of Node.js module.exports and how do you use it?

Question

What is the purpose of Node.js module.exports and how do you use it?

I can't seem to find any information on this, but it appears to be a rather important part of Node.js as I often see it in source code.

According to the Node.js documentation:

module

A reference to the current module. In particular module.exports is the same as the exports object. See src/node.js for more information.

But this doesn't really help.

What exactly does module.exports do, and what would a simple example be?

Answer 1

module.exports is the object that's actually returned as the result of a require call.

The exports variable is initially set to that same object (i.e. it's a shorthand "alias"), so in the module code you would usually write something like this:

let myFunc1 = function() { ... }; let myFunc2 = function() { ... }; exports.myFunc1 = myFunc1; exports.myFunc2 = myFunc2; 

to export (or "expose") the internally scoped functions myFunc1 and myFunc2.

And in the calling code you would use:

const m = require('./mymodule'); m.myFunc1(); 

where the last line shows how the result of require is (usually) just a plain object whose properties may be accessed.

NB: if you overwrite exports then it will no longer refer to module.exports. So if you wish to assign a new object (or a function reference) to exports then you should also assign that new object to module.exports

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It's worth noting that the name added to the exports object does not have to be the same as the module's internally scoped name for the value that you're adding, so you could have:

let myVeryLongInternalName = function() { ... }; exports.shortName = myVeryLongInternalName; // add other objects, functions, as required 

followed by:

const m = require('./mymodule'); m.shortName(); // invokes module.myVeryLongInternalName