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

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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,white20 alert(student.name);//fsdf21 alert(student.colors);//red,blue,white,black

寄生组合模式

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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);//undefined29 alert(student.name);//fsdf30 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。