call 和 apply的使用

call

  /**
     * 改变this指向
     * */
    function People(){
        this.name = "--";
        this.age = 0;
        this.show = function(){
            console.log(this.name,'今年',this.age,"岁");
        }
    }
    function Man(name, age){
        this.name = name;
        this.age = age;
    }
    var people = new People();
    var man = new Man("小明",25);
    people.show(); // -- 今年 0 岁
    people.show.call(man); //小明 今年 25 岁

   /**
     * 继承
     * */
    function People(name){
        this.name = name;
        this.showName = function(){
            console.log(this.name);
        }
    }
    function Man(name,song){
        //继承 People
        this.song = song;
        People.call(this,name);
    }
    // 自己的特长（原型方法）
    Man.prototype.sing = function(){
        console.log("爱唱",this.song);
    }
    var man = new Man("朱元璋","光辉岁月");
    man.showName(); //朱元璋
    man.sing();// 爱唱 光辉岁月

apply

   /**
     * 改变this指向
     * */
    function People(){
        this.name = "--";
        this.age = 0;
        this.show = function(){
            console.log(this.name,'今年',this.age,"岁");
        }
    }
    function Man(name, age){
        this.name = name;
        this.age = age;
    }
    var people = new People();
    var man = new Man("小明",25);
    people.show(); // -- 今年 0 岁
    people.show.apply(man); //小明 今年 25 岁

    /**
     * 继承
     * */
    function People(name){
        this.name = name;
        this.showName = function(){
            console.log(this.name);
        }
    }
    function Man(name,song){
        //继承 People
        this.song = song;
        People.apply(this,[name]);//注意区别
    }
    // 自己的特长（原型方法）
    Man.prototype.sing = function(){
        console.log("爱唱",this.song);
    }
    var man = new Man("朱元璋","光辉岁月");
    man.showName(); //朱元璋
    man.sing();// 爱唱 光辉岁月

两者之间的却别

1、call是多个参数，apply是两个参数（第二个参数数组的方式传递）

a.call(b,arg1,arg2…)

apply(b,[arg1,arg2]) //apply只有2个参数，它将call的参数（arg1,arg2…）放在一个数组中作为apply的第二参数

2、对一些对象方法的调用，比如数组的forEach的调用

 call的方法

[].forEach.call('1,2,3',function(item){console.log(item)}); // 1,2,3

apply同样使用会报错

[].forEach.call('1,2,3',function(item){console.log(item)}); // VM777:1 Uncaught TypeError: undefined is not a function(…)