apply,bind,call应用小总结

三者的作用都是改变函数执行时的上下文，也就是改变this指向
fun.apply(thisArg, [argsArray])
function.call(thisArg, arg1, arg2, …)
fun.bind(thisArg[, arg1[, arg2[, …]]])

call与apply的区别在于,传递参数的方式
bind与他们的区别是,bind是返回这个函数的copy，而call与apply是直接执行

一些应用：
求最大最小值
利用apply,call来做继承
调用匿名函数

一、call && apply

//一、最大最小
Math.min.apply(Math,[(3,5,6)]) == 6 //为什么

Math.min.apply(Math,{ 'length': 2, '0': '1', '1': '2' }) ==1

//二、将伪数组转化为数组
var arrayLike = { 'length': 2, '0': '1', '1': '2' };
//（必须以数字为属性，必须有length属性,length多了，就会多加undefined,length少了主动删减多余的）
var arr = Array.prototype.slice.call(arrayLike);
//arr为 ["1", "2"]
var arrayLike = { 'length': 3, '0': '1', '1': '2' };//arr为 ["1", "2"，undefined]
var arrayLike = { 'length': 1, '0': '1', '1': '2' };//arr为 ["1"]

//三、数组追加
var arr1 = [1,2];
var arr2 = [3,4];
[].push(arr1,arr2);
//arr1 [1,2,3,4] ; arr2[3,4]

//四、判断变量类型
function isArray(obj){
    return Object.prototype.toString.call(obj)
    == '[object Array'];
}
isArray([]) //true

//五、调用匿名函数
var animals = [
  { species: 'Lion', name: 'King' },
  { species: 'Whale', name: 'Fail' }
];

for (var i = 0; i < animals.length; i++) {
  (function(i) {
    this.print = function() {
      console.log('#' + i + ' ' + this.species
                  + ': ' + this.name);
    }
    this.print();
  }).call(animals[i], i);
}

二、bind

//1、创建绑定函数

this.x = 9;    // this refers to global "window" object here in the browser
var module = {
  x: 81,
  getX: function() { return this.x; }
};

module.getX(); // 81

var retrieveX = module.getX;
retrieveX();   
// returns 9 
var boundGetX = retrieveX.bind(module);
boundGetX(); // 81

//2、预传递参数

function list() {
  return Array.prototype.slice.call(arguments);
}
var list1 = list(1, 2, 3); // [1, 2, 3]
var leadingThirtysevenList = list.bind(null, 37);

var list2 = leadingThirtysevenList(); 
// [37]

var list3 = leadingThirtysevenList(1, 2, 3);
// [37, 1, 2, 3]

//3.有setTimeout时,this会自动指向window，用bind改变

function LateBloomer() {
  this.petalCount = Math.ceil(Math.random() * 12) + 1;
}

LateBloomer.prototype.bloom = function() {
  window.setTimeout(this.declare.bind(this), 1000);
};

LateBloomer.prototype.declare = function() {
  console.log('I am a beautiful flower with ' +
    this.petalCount + ' petals!');
};

var flower = new LateBloomer();
flower.bloom();  
// after 1 second, triggers the 'declare' methodfunction LateBloomer() {
  this.petalCount = Math.ceil(Math.random() * 12) + 1;
}

// Declare bloom after a delay of 1 second
LateBloomer.prototype.bloom = function() {
  window.setTimeout(this.declare.bind(this), 1000);
};
//this均指向LateBloomer这个自定义对象，
//LateBloomer {petalCount: a number of [1,13]}

LateBloomer.prototype.declare = function() {
  console.log('I am a beautiful flower with ' +
    this.petalCount + ' petals!');
};

var flower = new LateBloomer();
flower.bloom();  
// after 1 second, triggers the 'declare' method