打包原理

let modules += `${mod.id}: [
  function (require, module, exports) { ${mod.code} },
  ${JSON.stringify(mod.mapping)},
],`

(function(modules) {
  function require(id) {
    const [fn, mapping] = modules[id];

    function localRequire(name) {
      return require(mapping[name]);
    }

    const module = { exports : {} };

    fn(localRequire, module, module.exports);

    return module.exports;
  }

  require(0);
})({${modules}})