理解对象和创建对象

理解对象
对象有两种属性数据属性和访问器属性
数据属性有Configurable,Enumberable,Writable,Value四个描述行为的特性，访问器属性有Configurable,Enumberable,Get,Set四个描述行为的特性,可以通过Object.defineProperty()和Object.defineProperties()的方法重新定义这些特性
读取属性的特性：Object.getOwnPropertyDescriptor()
创建对象
工厂模式

function createPerson(name, age, job){
    var o = new Object();
    o.name = name;
    o.age = age;
    o.job = job;
    o.sayName = function(){
        alert(this.name);
    };    
    return o;
}

var person1 = createPerson("Nicholas", 29, "Software Engineer");
var person2 = createPerson("Greg", 27, "Doctor");

构造函数模式
用于定义实例属性

function Person(name, age, job){
    this.name = name;
    this.age = age;
    this.job = job;
    this.sayName = function(){
        alert(this.name);
    };    
}

var person1 = new Person("Nicholas", 29, "Software Engineer");
var person2 = new Person("Greg", 27, "Doctor");

原型模式
用于定义方法和共享的属性

function Person(){
}

Person.prototype.name = "Nicholas";
Person.prototype.age = 29;
Person.prototype.job = "Software Engineer";
Person.prototype.sayName = function(){
    alert(this.name);
};

var person1 = new Person();

组合使用构造函数和原型模式（最常用）

function Person(name, age, job){
    this.name = name;
    this.age = age;
    this.job = job;
    this.friends = ["Shelby", "Court"];
}

Person.prototype = {
    constructor: Person,
    sayName : function () {
        alert(this.name);
    }
};

var person1 = new Person("Nicholas", 29, "Software Engineer");
var person2 = new Person("Greg", 27, "Doctor");
 person1.friends.push("Van");       
alert(person1.friends);    //"Shelby,Court,Van"
alert(person2.friends);    //"Shelby,Court"
alert(person1.friends === person2.friends);  //false
alert(person1.sayName === person2.sayName);  //true

寄生构造函数模式
多数用于改造已存在的对象

function SpecialArray(){       
   //create the array
   var values = new Array();
   
   //add the values
   values.push.apply(values, arguments);
   
   //assign the method
   values.toPipedString = function(){
       return this.join("|");
   };
   
   //return it
   return values;        
}

var colors = new SpecialArray("red", "blue", "green");
alert(colors.toPipedString()); //"red|blue|green"

alert(colors instanceof SpecialArray);