实现一个myCall

• 名词解释：call() 方法使用一个指定的 this 值和单独给出的一个或多个参数来调用一个函数。
• 原生方法：Function.prototype.call()

1. 先看一下原生方法的调用

let obj = {
  name: "jay chou",
  getName: function () {
    console.log(this.name);
  },
  getNameAge(age) {
    console.log(this.name + " " + age);
  },
};

let obj2 = {
  name: "Jolin Tsai",
};

obj.getName.call(obj2); //Jolin Tsai
obj.getNameAge.call(obj2, 40); //Jolin Tsai 40

2. 自己实现一个myCall方法

let obj = {
  name: "jay chou",
  getName: function () {
    console.log(this.name);
  },
  getNameAge(age) {
    console.log(this.name + " " + age);
  },
};

let obj2 = {
  name: "Jolin Tsai",
};

Function.prototype.myCall = function (context, ...arg) {
  const _this =
    typeof context == "object" ? (context ? context : window) : window;
  const key = Symbol();
  _this[key] = this;
  _this[key](...arg);
  delete _this[key];
};

obj.getName.myCall(obj2);//Jolin Tsai
obj.getNameAge.myCall(obj2, 40);//Jolin Tsai 40
obj.getNameAge.myCall(1, 40);// 40
obj.getNameAge.myCall("1234", 40);// 40
obj.getNameAge.myCall(["1234"], 40);// undefined 40
obj.getNameAge.myCall(new Date(), 40);// undefined 40
obj.getNameAge.myCall(new RegExp("/BB/"), 40); //undefined 40

function Person(name) {
  this.name = name;
  console.log("姓名:" + this.name);
}

Person.myCall(null, "jay"); //姓名:jay
let person = new Person("jolin"); //姓名:jolin
obj.getName.myCall(person); //jolin