call、apply和bind

call、apply作用：
调用函数，改变函数的this指向
bind作用：
不会调用函数，改变函数this指向，返回原函数改变this之后产生的新函数

       function fn(x, y) {
            console.log(this);
            console.log(x + y);
        }
        var o = {
            name: 'andy'
        };
      fn.call(o, 1, 2);
    // 此时这个函数的this 就指向了o这个对象，1、2当形参传递
      fn.apply(o,[1,2]) //参数使用数组传递 运行结果为3

call实现继承

function Father(name, age) {
            this.name = name;
            this.age = age;
        }
        Father.prototype.money = function() {
            console.log('father earns money');
        }

        function Son(name, age, score) {
            Father.call(this, name, age);
             // this 指向子构造函数的对象实例
            //把father中this指向son里面this
            this.score = score;
        }
        Son.prototype = new Father();
        Son.prototype.constructor = Son;
        // 重新指回原来的构造函数
        Son.prototype.exam = function() {
            console.log('son needs exam')
        }

        var xiaoming = new Son('xiaoming', '18', '90')
        xiaoming.exam() //son needs exam
        xiaoming.money() //father earns money

call添加数组

        let arr1 = ['1', '2'];
        (function() {
            Array.prototype.push.call(arguments, '王五');
            console.log(arguments);
        })(arr1)
        // 0: Array(2) ["1", "2"]
        // 1: "王五"

apply合并数组

    let arr1=[1,2,3]; 
    let arr2=[4,5,6]; 
    Array.prototype.push.apply(arr1,arr2); //将arr2合并到了arr1中

apply求数组最大值

    var arr = [1, 66, 3, 99, 4];
    var max = Math.max.apply(Math, arr);
    var max1 = Math.max.apply(null, arr);

bind实用

        var btns = document.querySelectorAll('button');
             for (var i = 0; i < btns.length; i++) {
                    btns[i].onclick = function() {
                        this.disabled = true;
                        setTimeout(function() {
                              this.disabled = false;
                        }.bind(this), 2000);  //2秒后解除按钮禁用
                  }
            }  //让定时器里面的this指向btn

bind改变this指向

        var name = '李四'
        var foo = {
            name: "张三",
            logName: function(age) {
                console.log(this.name, age);
            }
        }
        foo.logName(8) //张三 8

        var fooNew = foo.logName;
        fooNew(10) //李四,10

        var fooNewBind = foo.logName.bind(foo);
        fooNewBind(11) //张三,11  因为bind改变了fooNewBind里面的this指向