call apply  bind

            相同点： 都可以改变this指向     

         不同点： apply的第二个参数是 数组 

         不同点：  bind需要二次调用

        var obj = {

            name:'zhangsan',

            say:function(str,str2){

                console.log(this.name+' '+str+' '+str2)  // this  {name:'李二'}

            }

        }

        // obj.say('hello')

        // obj.say.call({name:'李二'},'hello','world');// obj.say 函数中的 this 变成了{name:'李二'’}

        // obj.say.apply({name:'李二'},['hello','world'])

       var f =  obj.say.bind({name:'李二'},'hello','world');

       f();

        // var obj2 = {

        //     name:'王武',

        //     setname:function(){

        //         // console.log(this);  //this  obj2

        //         obj.say.call(this);  // obj2:{}

        //     }

        // }

        // obj2.setname();