call和apply方法

/*
* @ call和apply方法
* @ 當一個object沒有某個方法，可是其餘的有，咱們能夠藉助call或apply用其它對象的方法來操做。
* @ (有方法的)對象.call("環境的上下文本對象",參數)
* @ 經過call和apply，咱們能夠實現對象繼承。示例
*/
    /*function product(test){
        alert(test);
    }


    function log(){

    }
    product.call(log,2);*/



    /*function product(test){
        alert(test);
    }


    function log(){
        product.call(this,2);
    }
    log();*/


    function Product(name, price){
        this.name = name;
        this.price = price;

        if(price < 0){
            throw RangeError('Cannot create product ' + this.name + ' with a negative price');
        }
    }

    // call方法
    function Food(name,price){
        Product.call(this,name,price);
        this.category = "food";
    }

    // 等同於
    function Food(name,price){
        this.name = name;
        this.price = price;

        if(price < 0){
            throw RangeError('Cannot create product ' + this.name + ' with a negative price');
        }

        this.category = "food";
    }

    // 以DOM爲例子
    /*function changeStyle(attr, value){
        this.style[attr] = value;
    }
    var box = document.getElementById('box');

    window.changeStyle.call(box, "height", "200px");

    window.changeStyle.apply(box, ['height', '200px']);*/


    /*// 實現繼承
    var Parent = function(){
        this.name = "yc",
        this.age = "1"
    }

    var child = {};
    Parent.call(child);     // 實現繼承*/




    /*log("%c紅色的字, %c綠色的字, %c大象", "color:red", "color:green", "line-height:100px;padding:50px;background:url(http://fanjs.net/res/img/favicon.ico");*/

    function say(name){
        console.log(this + "," + name);
    }
    say.call2 = function( thisObj, arg1 ) {
        thisObj = new Object( thisObj );
        thisObj.say = this;
        return thisObj.say(arg1);
    };

    say.call2("hola","Mike");


/*
* object.prototype.call
* @ 當一個object沒有某個方法，可是其餘的有，咱們能夠藉助call或apply用其它對象的方法來操做。
* @ 語法: fun.call(thisArg[, arg1[, arg2[, ...]]])
* @ param: thisArg {object}     //當前引用對象
*   @ 不傳參數,傳null,undefined, this指向window對象
*   @ 傳遞另外一個函數的函數名fun2, this指向函數fun2的引用
*   @ 傳遞一個對象,函數中的this指向這個對象
*   @ 值爲原始值(數字,字符串,布爾值), this會指向該原始值的自動包裝對象,如String,Number,Boolean
* @ param: arg1, arg2, ... {object}       // arguments參數
*/

// call函數中的this指向
function a(){
    console.log(this);
}
function b(){}

var objthis = {name: "Alan"};           //定義對象
a.call();               // window
a.call(null);           // window
a.call(undefined);      // window
a.call(1);              // Number {[[PrimitiveValue]]: 1}
a.call("");             // String {length: 0, [[PrimitiveValue]]: ""}
a.call(true);           // Boolean {[[PrimitiveValue]]: true}
a.call(b);              // function b(){}
a.call(objthis);        // Object {name: "Alan"}


// 使用call對象的構造函數鏈
function Product(name, price){
    this.name = name;
    this.price = price;

    if(price < 0){
        throw RangeError("Cannot create product " + this.name + " with negative price");
    }
}

function Food(name,price){
    Product.call(this,name,price);
    this.category = "food"
}
var cheese = new Food("feta",5);

// 使用call調用匿名函數
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);

    // 等同於
    /*(function(){
        this.print = function(){
            console.log("#" + i + " " + animals[i].species + ": " + animals[i].name);
        }
        this.print();
    })();*/
}

// 使用call調用函數的上下文this
function greet(){
    var reply = [this.person, "Is An Awesome", this.role].join(" ");
    console.log(reply);
}

var obj = {
    person: "Douglas Crockford", role: "Javascript Developer"
};

greet.call(obj);