apply，call ，bind 区别用法

apply call bind 共同点

1. 都是用来改变函数的this对象的指向的。
2. 第一个参数都是this要指向的对象。
3. 都可以利用后续参数传参

apply

语法：apply(thisArg, [argsArray])

var user = {
  greet: "hello",
  greetUser: function (userName) {
    console.log(this.greet + " " + userName);
  },
};

var greetHi = {
  greet: "hi",
};

user.greetUser.apply(greetHi, "zhouJin"); // hi zhouJin

call

语法：call(thisArg, [argsArray])

var user = {
  greet: "hello",
  greetUser: function (userName) {
    console.log(this.greet + " " + userName);
  },
};

var greetHi = {
  greet: "hi",
};

user.greetUser.call(greetHi, "zhouJin"); // hi zhouJin

bing

用法: 使用bind方法，可以为函数绑定this值，然后作为一个新的函数返回

var user = {
  greet: "hello",
  greetUser: function (userName) {
    console.log(this.greet + " " + userName);
  },
};

var greetHi = user.greetUser.bind({ greet: "hi" });

greetHi("zhouJin"); // hi zhouJin