Trantor Liu Trantor Liu - 2 months ago 7
Javascript Question

How does require() in node.js work?

I tried this:

// mod.js
var a = 1;
this.b = 2;
exports.c = 3;

// test.js
var mod = require('./mod.js');
console.log(mod.a); // undefined
console.log(mod.b); // 2
console.log(mod.c); // 3, so this === exports?


So I image that require() may be implement like this:

var require = function (file) {
var exports = {};
var run = function (file) {
// include "file" here and run
};
run.apply(exports, [file]);
return exports;
}


Is that right? Please help me to understand require(), or where can I find the source code. Thanks!

Answer

Source code is here. exports/require are not keywords, but global variables. Your main script is wrapped before start in a function which has all the globals like require, process etc in its context.

Note that while module.js itself is using require(), that's a different require function, and it is defined in the file called "node.js"

Side effect of above: it's perfectly fine to have "return" statement in the middle of your module (not belonging to any function), effectively "commenting out" rest of the code