javascript中的继承

原型链模式和组合继承模式的区别就在于：继承模式中调用了两次基类的构造函数，结果实例中的属性就屏蔽了原型中的同名属性(这样做可以避免各个实例共享的引用实例相互影响)。组合继承是javascript中最常用的继承模式。

例如

View Code

 1 function Person(name){
 2     this.name = name;
 3     this.colors = ["red","blue","white"];
 4 }
 5 Person.prototype.sayName = function(){
 6     return this.name;
 7 }
 8 function Student(name,age){
 9     Person.call(this,name);//组合模式中需要这句
10     this.age = age;    
11 }
12 Student.prototype = new Person();
13 Student.prototype.sayAge = function(){
14     return this.age;
15 }
16 var student = new Student("fsdf",12);
17 student.colors.push("black");
18 
19 alert(Student.prototype.colors);//red,blue,white
20 alert(student.name);//fsdf
21 alert(student.colors);//red,blue,white,black

寄生组合模式

View Code

 1 function object(o){
 2    function F(){}
 3    F.prototype = 0;
 4    return new F();   
 5 }
 6 function inheritPrototype(student,person){
 7    var prototype = object(person.prototype);
 8    prototype.constructor = student;
 9    student.prototype = prototype;   
10 }
11 function Person(name){
12     this.name = name;
13     this.colors = ["red","blue","white"];
14 }
15 Person.prototype.sayName = function(){
16     return this.name;
17 }
18 function Student(name,age){
19     Person.call(this,name);
20     this.age = age;    
21 }
22 inheritPrototype(Student,Person);
23 Student.prototype.sayAge = function(){
24   alert(this.age);
25 }
26 var student = new Student("fsdf",12);
27 student.colors.push("black");
28 alert(Student.prototype.colors);//undefined
29 alert(student.name);//fsdf
30 alert(student.colors);//red,blue,white,black

比较两种模式，很容易发现在寄生组合模式中Student.prototype上面没有创建不必要的属性name和colors，从而提高了效率，同时原型链保持不变。开发人员普遍认为寄生组合式继承是引用类型最理想的继承方式。

YUI的YAHOO.lang.extend()方法采用的就是寄生组合继承。