node.js 中的 require() 是如何工作的? [英] How does require() in node.js work?

问题描述

我试过了:

// 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?

所以我认为 require() 可能是这样实现的:

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;
}

是吗?请帮助我理解require()，或者我在哪里可以找到源代码.谢谢！

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

推荐答案

源代码是 此处.exports/require 不是关键字，而是全局变量.您的主要脚本是 在 start 在一个函数中，该函数具有require、process 等在其上下文中.

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.

请注意，虽然 module.js 本身使用的是 require()，但这是一个不同的 require 函数，它是 定义在名为node.js"的文件中

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"

上面的副作用:在你的模块(不属于任何函数)中间有return"语句是完全没问题的，有效地注释掉"其余的代码

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

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