User 类被编译以后转化为构造函数。被编译后生成了 _classCallCheck , _instanceof 方法。 class User{ } const user = new User(); console.log(user); // {} //↑↑↑↑↑↑↑↑↑↑↑↑↑ ES6 ↑↑↑↑↑↑↑↑↑↑↑↑↑↑ //↓↓↓↓↓↓↓↓↓↓↓↓↓ ES5 ↓↓↓↓↓↓↓↓↓↓↓↓↓↓ "use strict"; function _instanceof(left, right) { if...
