JS面向对象的详细介绍（二）

console.log('---- 返回字符串 start ----');var Person = function(){this.name = '王大锤';return '罗小虎';
}var per = new Person();for (var item in per){
    console.log( item + ': ' + per[item] );
}//---- 返回字符串 start ----//name: 王大锤console.log('----- 返回对象 start ----');var PersonTwo = function(){this.name = '倚天剑';return {nickname: '屠龙刀', price: 9999 };
}var per2 = new PersonTwo();for (var item in per2){
    console.log(item + ': ' + per2[item]);
}//----- 返回对象 start ----//nickname: 屠龙刀//price: 9999

var Person = function(){ 
    console.log( this == window );  //truethis.price = 5188; 
}var per = Person();
console.log(price); //5188console.log(per);  //undefinedconsole.log('......_-_'); //......_-_console.log(per.price); //Uncaught TypeError: Cannot read property 'helloPrice' of undefined

var Person = function(){ 'use strict';
    console.log( this );  //undefinedthis.price = 5188; //Uncaught TypeError: Cannot set property 'helloPrice' of undefined}var per = Person();

var Person = function(){ //先判断this是否为Person的实例对象，不是就new一个if (!(this instanceof Person)){return new Person();
    }
    console.log( this );  //Person {}this.price = 5188; 
}var per = Person(); 
console.log(per.price); //5188

var Person = function(){
    console.log('1111'); 
    console.log(this); this.name = '王大锤';this.age = 18;this.run = function(){
        console.log('this is Person的实例对象吗：' + (this instanceof Person) ); 
        console.log(this); 
    }
}var per = new Person();
per.run();/* 打印日志：
1111
Person {}
this is Person的实例对象吗：true
Person {name: "王大锤", age: 18, run: function}*/console.log('---------------');var Employ = {
    email: 'cnblogs@sina.com',
    name: '赵日天',
    eat: function(){
        console.log(this);
    }
}

console.log(Employ.email + ', ' + Employ.name);
Employ.eat();/* 打印日志：
---------------
cnblogs@sina.com, 赵日天
Object {email: "cnblogs@sina.com", name: "赵日天", eat: function}*/

var A = { 
    name: '王大锤', 
    getInfo: function(){return '姓名：' + this.name;
    } 
}var B = { name: '赵日天' };

B.getInfo = A.getInfo;
console.log( B.getInfo() ); //姓名：赵日天//A.getInfo属性赋给B, 于是B.getInfo就表示getInfo方法所在的当前对象是B, 所以这时的this.name就指向B.name

//1、多层中的this (错误演示)var o = {
    f1: function(){
        console.log(this); //这个this指的是o对象var f2 = function(){
            console.log(this);
        }();//由于写法是(function(){ })() 格式， 则f2中的this指的是顶层对象window    }
}

o.f1();/* 打印日志：
Object {f1: function}

Window {stop: function, open: function, alert: function, confirm: function, prompt: function…}*///2、上面代码的另一种写法（相同效果）var temp = function(){
    console.log(this);
}var o = {
    f1: function(){
        console.log(this); //这个this指o对象var f2 = temp(); //temp()中的this指向顶层对象window    }
}
o.f1(); 
/* 打印日志
Object {f1: function}

Window {stop: function, open: function, alert: function, confirm: function, prompt: function…}*///表示上面两种写法是一样的效果，this的错误演示//3、多层中this的正确使用：使用一个变量来固定this对象，然后在内层中调用该变量var o = {
    f1: function(){
        console.log(this); //o对象var that = this;var f2 = function(){
            console.log(that); //这个that指向o对象        }();
    }
}
o.f1();/* 打印日志：
Object {f1: function}
Object {f1: function}*/

//1、多层中数组遍历中this的使用 （错误演示）var obj = {
    email: '大锤@sina.com', 
    arr: ['aaa', 'bbb', '333'],
    fun: function(){//第一个this指的是obj对象this.arr.forEach(function(item){//这个this指的是顶层对象window， 由于window没有email变量，则为undefinedconsole.log(this.email + ': ' + item);
        });
    }
}

obj.fun(); 
/* 打印结果：
undefined: aaa
undefined: bbb
undefined: 333 *///2、多层中数组遍历中this的使用 （正确演示，第一种写法）var obj = {
    email: '大锤@sina.com', 
    arr: ['aaa', 'bbb', '333'],
    fun: function(){//第一个this指的是obj对象var that = this; //将this用变量固定下来this.arr.forEach(function(item){//这个that指的是对象objconsole.log(that.email + ': ' + item);
        });
    }
}
obj.fun(); //调用/* 打印日志：
大锤@sina.com: aaa
大锤@sina.com: bbb
大锤@sina.com: 333 *///3、多层中数组遍历中this正确使用第二种写法：将this作为forEach方法的第二个参数，固定循环中的运行环境var obj = {
    email: '大锤@sina.com', 
    arr: ['aaa', 'bbb', '333'],
    fun: function(){//第一个this指的是obj对象this.arr.forEach(function(item){//这个this从来自参数this, 指向obj对象console.log(this.email + ': ' + item);
        }, this);
    }
}
obj.fun(); //调用/* 打印日志：
大锤@sina.com: aaa
大锤@sina.com: bbb
大锤@sina.com: 333 */

var obj = {};var f = function(){
    console.log(this);return this;
}

console.log('....start.....');
f();
f.call();
f.call(null);
f.call(undefined);
f.call(window);
console.log('**** call方法的参数如果为空、null和undefined， 则默认传入全局等级window；如果call方法传入自定义对象obj，则函数f会在对象obj的作用域中运行 ****');
f.call(obj);
console.log('.....end.....');/* 打印日志：
....start.....
Window {stop: function, open: function, alert: function, confirm: function, prompt: function…}
Window {stop: function, open: function, alert: function, confirm: function, prompt: function…}
Window {stop: function, open: function, alert: function, confirm: function, prompt: function…}
Window {stop: function, open: function, alert: function, confirm: function, prompt: function…}
Window {stop: function, open: function, alert: function, confirm: function, prompt: function…}
**** call方法的参数如果为空、null和undefined， 则默认传入全局等级window；如果call方法传入自定义对象obj，则函数f会在对象obj的作用域中运行 ****
Object {}
.....end.....*/