call 与 apply 的区别是 cal 只能一个一个的传递参数，apply 是可以通过数组来传递参数, bind 需要进行一次额外的声明，
call 实例
var arr = {num: 2};function aa(val1, val2) { return this.num+val1+val2;}console.log(aa.call(arr, 2,3)); // functionname.call(obj, functionArguments)apply 实例
var obj = {num: 2};var obj2 = {num: 3};function add(val1, val2, val3) { return this.num+val1+val2+val3;}var arr = [1,2,3];console.log(add.apply(obj, arr));console.log(add.apply(obj2, arr));bind 实例
var obj = {num: 5};function add(val1, val2, val3) { return this.num+val1+val2+val3; } var bound = add.bind(obj); console.log(bound(3,4,5));
