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CommonJS 模块化规范

定义

https://github.com/nodejs/node/blob/master/lib/internal/modules/cjs/loader.js

  • commonJS 是一个运行时解析的规范
  • require 不是关键字，它类似一个全局函数

实现一个 customRequire

  • moduleA.js 
console.log('this is module A');

module.exports = 123;
  • module.js 
const moduleA = require('./moduleA.js');

console.log('this is module', moduleA);
  • index.js
const vm = require('vm');
const path = require('path');
const fs = require('fs');

function customRequire(filePath) {
  // 1. 读取文件内容
  const absPath = path.resolve(__dirname, filePath);
  const content = fs.readFileSync(absPath, 'utf-8');

  const wrapper = [
    '(function(require, module, exports) {',
    '})'
  ];

  // 2. 将字符串变成可执行函数
  const wrappedContent = wrapper[0] + content + wrapper[1];
  const script = new vm.Script(wrappedContent, {
    filename: 'index.js'
  });
  const func = script.runInThisContext();

  // 3. 声明 module.exports，执行函数
  const module = {
    exports: {}
  };
  func(customRequire, module, module.exports);

  return module.exports;
}

customRequire('./module.js');