https://nodejs.org/dist/latest-v12.x/docs/api/modules.html#modules_exports_shortcut

function require(/* ... */) {
  const module = { exports: {} };
  ((module, exports) => {
    // Module code here. In this example, define a function.
    function someFunc() {}
    exports = someFunc;
    // At this point, exports is no longer a shortcut to module.exports, and
    // this module will still export an empty default object.
    module.exports = someFunc;
    // At this point, the module will now export someFunc, instead of the
    // default object.
  })(module, module.exports);
  return module.exports;
}

nodejs 的 require 遇到 js 文件的时候会调用内部的 vm 模块，我追源码追到 这里 就看不懂了……