js创建对象和继承

一、创建对象

1、组合模式（构造函数模式和原型模式）：构造函数用于定义实例属性，而原型模式用于定义方法和共享属性。

function Person(name ,age,job){
this.name = name;
this.age = age;
this.job = job;
this.friends = ['a','b','c'];
}
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

2、动态原型模式

function Person(name,age,job){
this.name =name;
this.age = age;
this.job = job;
if(typeof this.sayName != "function"){
Person.prototype.sayName = function (){
alert(this.name);
};
}
var person1 = new Person("nic","20","soft");

二、继承（js主要通过原型链实现继承）

1、组合继承：使用原型链实现对原型属性和方法的继承，而通过构造函数实现实例属性的继承

function SuperType(name){
this.name = name;
this.colors = ["red", "blue", "green"];
}

SuperType.prototype.sayName = function(){
alert(this.name);
};

function SubType(name, age){
SuperType.call(this, name);  ////第二次调用SuperType()

this.age = age;
}

SubType.prototype = new SuperType(); //第一次调用SuperType()
SubType.prototype.constructor = SubType;
SubType.prototype.sayAge = function(){
alert(this.age);
};

var instance1 = new SubType("Nicholas", 29);
instance1.colors.push("black");
alert(instance1.colors);  //"red,blue,green,black"
instance1.sayName();      //"Nicholas";
instance1.sayAge();       //29

var instance2 = new SubType("Greg", 27);
alert(instance2.colors);  //"red,blue,green"
instance2.sayName();      //"Greg";
instance2.sayAge();       //27

2、寄生组合式继承：不必为了指定子类型的原型而调用超类型的构造函数，所需要的无非就是超类型原型的一个副本。

function object(o){
function F(){}
F.prototype = o;
return new F();
}

function inheritPrototype(subType, superType){
var prototype = object(superType.prototype);   //create object
prototype.constructor = subType;               //augment object
subType.prototype = prototype;                 //assign object
}

function SuperType(name){
this.name = name;
this.colors = ["red", "blue", "green"];
}

SuperType.prototype.sayName = function(){
alert(this.name);
};

function SubType(name, age){
SuperType.call(this, name);

this.age = age;
}

inheritPrototype(SubType, SuperType);

SubType.prototype.sayAge = function(){
alert(this.age);
};

var instance1 = new SubType("Nicholas", 29);
instance1.colors.push("black");
alert(instance1.colors);  //"red,blue,green,black"
instance1.sayName();      //"Nicholas";
instance1.sayAge();       //29

var instance2 = new SubType("Greg", 27);
alert(instance2.colors);  //"red,blue,green"
instance2.sayName();      //"Greg";
instance2.sayAge();       //27