call、apply

1.call和apply的区别

apply传入数组，call依次传入参数，两者第一个参数都是this

2.用途

1).改变this指向

name = "tom";

var obj1 = {
    name: "anne",
    getName(){
        console.log(this.name);
    }
};

var obj2 = {
    name: "seven"
};

var getName = function(){
    console.log("this.name:",this.name);
}

getName();              //tom
getName.call(obj1);     //anne
getName.call(obj2);     //seven

obj1.getName.call(obj2);     //seven

//修正this的指向
document.getElementById( 'div1' ).onclick = function(){ 
    var func = function(){ 
        alert ( this.id );
    } 
    func.call( this );  // 输出：div1 
};

2).bind的实现

Function.prototype.bind = function( context ){
    var self = this;
    return function(){
        //返回对象的时候，this指向该对象
        return self.apply( context, arguments );
    }
};

var obj = {
    name: 'sven'
}

var func = function(){
    console.log(this.name); //sven
};

func().bind(obj);

3).借用其他对象的方法

var A = function( name ){
    this.name = name;
}

var B = function(){
    A.apply(this, arguments);
}

B.prototype.getName = function(){
    return this.name;
}

var b = new B('sevn');
console.log(b.getName()); //'sven'


//对象借用数组的push方法
var a = {};
Array.prototype.push.call(a,'first');
console.log(a);  //{ '0': 'first', length: 1 }