new 的原理

1function _new(fn, ...arg) {
2    const obj = Object.create(fn.prototype);
3    const newObj = fn.apply(obj, arg);
4    return newObj instanceof Object ? newObj : obj;
5}
6
7// 使用的例子：
8function GirlFirend(name, age) {
9    this.name = name;
10    this.age = age;
11    this.sayName = function () {
12        console.log(this.name);
13    };
14}
15const xiaoMei = _new(GirlFirend, "Xiao Mei", 18)
16console.log(xiaoMei)  // GirlFirend {name: "Xiao Mei", age: 18, sayName: ƒ}