參考地址（this相關(guān)問題）

http://www.liaoxuefeng.com/wiki/001434446689867b27157e896e74d51a89c25cc8b43bdb3000/0014345005399057070809cfaa347dfb7207900cfd116fb000

對象的定義

var xiaoming = {
    name: '小明',
    birth: 1990
};

var xiaoming = {
    name: '小明',
    birth: 1990,
    age: function () {
        var y = new Date().getFullYear();
        return y - this.birth;
    }
};

xiaoming.age; // function xiaoming.age()
xiaoming.age(); // 今年調(diào)用是25,明年調(diào)用就變成26了

function getAge() {
    var y = new Date().getFullYear();
    return y - this.birth;
}

var xiaoming = {
    name: '小明',
    birth: 1990,
    age: getAge
};

xiaoming.age(); // 25, 正常結(jié)果
getAge(); // NaN this指向全局對象勋陪，也就是window

要保證this指向正確，必須用obj.xxx()的形式調(diào)用

'use strict';

var xiaoming = {
    name: '小明',
    birth: 1990,
    age: function () {
        var y = new Date().getFullYear();
        return y - this.birth;
    }
};

var fn = xiaoming.age;
fn(); // Uncaught TypeError: Cannot read property 'birth' of undefined

this指針只在age方法的函數(shù)內(nèi)指向xiaoming，在函數(shù)內(nèi)部定義的函數(shù)论矾，this又指向undefined了４勒（在非strict模式下，它重新指向全局對象window)

'use strict';

var xiaoming = {
    name: '小明',
    birth: 1990,
    age: function () {
        function getAgeFromBirth() {
            var y = new Date().getFullYear();
            return y - this.birth;
        }
        return getAgeFromBirth();
    }
};

xiaoming.age(); // Uncaught TypeError: Cannot read property 'birth' of undefined

修復方法 that變量捕獲this

'use strict';

var xiaoming = {
    name: '小明',
    birth: 1990,
    age: function () {
        var that = this; // 在方法內(nèi)部一開始就捕獲this
        function getAgeFromBirth() {
            var y = new Date().getFullYear();
            return y - that.birth; // 用that而不是this
        }
        return getAgeFromBirth();
    }
};

xiaoming.age(); // 25

apply 指定函數(shù)的this指向哪個對象

function getAge() {
    var y = new Date().getFullYear();
    return y - this.birth;
}

var xiaoming = {
    name: '小明',
    birth: 1990,
    age: getAge
};

xiaoming.age(); // 25
getAge.apply(xiaoming, []); // 25, this指向xiaoming, 參數(shù)為空

apply()與call()區(qū)別

apply()把參數(shù)打包成Array再傳入；

call()把參數(shù)按順序傳入县匠。

Math.max(3, 5, 4)

Math.max.apply(null, [3, 5, 4]); // 5
Math.max.call(null, 3, 5, 4); // 5

裝飾器

統(tǒng)計一下代碼一共調(diào)用了多少次parseInt()

var count = 0;
var oldParseInt = parseInt; // 保存原函數(shù)

window.parseInt = function () {
    count += 1;
    return oldParseInt.apply(null, arguments); // 調(diào)用原函數(shù)
};

// 測試:
parseInt('10');
parseInt('20');
parseInt('30');
count; // 3