javascript中call apply 与 bind方法详解

function a(){
 //输出函数a中的this对象
 console.log(this); 
}
//定义函数b
function b(){} 

var obj = {name:'这是一个屌丝'}; //定义对象obj
a.call(); //window
a.call(null); //window
a.call(undefined);//window
a.call(1); //Number
a.call(''); //String
a.call(true); //Boolean
a.call(b);// function b(){}
a.call(obj); //Object

function greet() {
 var reply = [this.person, '是一个轻量的', this.role].join(' ');
 console.log(reply);
}

var i = {function greet() {
 var reply = [this.person, '是一个轻量的', this.role].join(' ');
 console.log(reply);
}

var i = {
 person: 'JSLite.io', role: 'Javascript 库。'
};

greet.call(i); 
// JSLite.io 是一个轻量的 Javascript 库。


 person: 'JSLite.io', role: 'Javascript 库。'
};

greet.call(i); 
// JSLite.io 是一个轻量的 Javascript 库。

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);
}
//#0 Lion: King
//#1 Whale: Fail

var a = {
 name:'JSLite.io', //定义a的属性
 say:function(){ //定义a的方法
 console.log("Hi,I'm function a!");
 }
};
function b(name){
 console.log("Post params: "+ name);
 console.log("I'm "+ this.name);
 this.say();
}

b.call(a,'test');
//Post params: test
//I'm onepixel
//I'm function a!

function jsy(x,y,z){
 console.log(x,y,z);
}

jsy.apply(null,[1,2,3]); 
// 1 2 3

Function.prototype.construct = function(aArgs) {
 var fConstructor = this, 
 fNewConstr = function() { 
 fConstructor.apply(this, aArgs); 
 };
 fNewConstr.prototype = fConstructor.prototype;
 return new fNewConstr();
};
function MyConstructor () {
 for (var nProp = 0; nProp < arguments.length; nProp++) {
 console.log(arguments,this)
 this["property" + nProp] = arguments[nProp];
 }
}
var myArray = [4, "Hello world!", false];
var myInstance = MyConstructor.construct(myArray);

console.log(myInstance.property1);  // logs "Hello world!"
console.log(myInstance instanceof MyConstructor); // logs "true"
console.log(myInstance.constructor);  // logs "MyConstructor"

//里面有最大最小数字值的一个数组对象
var numbers = [5, 6, 2, 3, 7];

/* 使用 Math.min/Math.max 在 apply 中应用 */
var max = Math.max.apply(null, numbers);
// 一般情况是用 Math.max(5, 6, ..) 或者 Math.max(numbers[0], ...) 来找最大值
var min = Math.min.apply(null, numbers);

//通常情况我们会这样来找到数字的最大或者最小值
//比对上面的栗子，是不是下面的看起来没有上面的舒服呢？
max = -Infinity, min = +Infinity;
for (var i = 0; i < numbers.length; i++) {
 if (numbers[i] > max)
 max = numbers[i];
 if (numbers[i] < min) 
 min = numbers[i];
}

function minOfArray(arr) {
 var min = Infinity;
 var QUANTUM = 32768;

 for (var i = 0, len = arr.length; i < len; i += QUANTUM) {
 var submin = Math.min.apply(null, arr.slice(i, Math.min(i + QUANTUM, len)));
 console.log(submin, min)
 min = Math.min(submin, min);
 }

 return min;
}

var min = minOfArray([5, 6, 2, 3, 7]);

var obj = {name:'JSLite.io'};
/**
 * 给document添加click事件监听，并绑定EventClick函数
 * 通过bind方法设置EventClick的this为obj，并传递参数p1,p2
 */
document.addEventListener('click',EventClick.bind(obj,'p1','p2'),false);
//当点击网页时触发并执行
function EventClick(a,b){
 console.log(
  this.name, //JSLite.io
  a, //p1
  b //p2
 )
}
// JSLite.io p1 p2

if (!Function.prototype.bind) {
 Function.prototype.bind = function (oThis) {
 if (typeof this !== "function") {
 // closest thing possible to the ECMAScript 5
 // internal IsCallable function
 throw new TypeError("Function.prototype.bind - what is trying to be bound is not callable");
 }

 var aArgs = Array.prototype.slice.call(arguments, 1), 
 fToBind = this, // this在这里指向的是目标函数
 fNOP = function () {},
 fBound = function () {
  return fToBind.apply(this instanceof fNOP
   "https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Function/bind#Compatibility">https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Function/bind#Compatibility

应用场景：继承




function Animal(name,weight){
 this.name = name;
 this.weight = weight;
}
function Cat(){
 // 在call中将this作为thisArgs参数传递
 // Animal方法中的this就指向了Cat中的this
 // 所以Animal中的this指向的就是cat对象
 // 在Animal中定义了name和weight属性，就相当于在cat中定义了这些属性
 // cat对象便拥有了Animal中定义的属性，从而达到了继承的目的
 Animal.call(this,'cat','50');
 //Animal.apply(this,['cat','50']);
 this.say = function(){
 console.log("I am " + this.name+",my weight is " + this.weight);
 }
}
//当通过new运算符产生了cat时，Cat中的this就指向了cat对象
var cat = new Cat();
cat.say();
//输出=> I am cat,my weight is 50




原型扩展


在原型函数上扩展和自定义方法，从而不污染原生函数。例如：我们在 Array 上扩展一个 forEach


function test(){
 // 检测arguments是否为Array的实例
 console.log(
 arguments instanceof Array, //false
 Array.isArray(arguments) //false
 );
 // 判断arguments是否有forEach方法
 console.log(arguments.forEach); 
 // undefined
 // 将数组中的forEach应用到arguments上
 Array.prototype.forEach.call(arguments,function(item){
 console.log(item); // 1 2 3 4
 });
}
test(1,2,3,4);