// Helper function to correctly set up the prototype chain for subclasses.

// Similar to `goog.inherits`, but uses a hash of prototype properties and

// class properties to be extended.

// 这里使用的函数表达式

var extend = function(protoProps, staticProps) {

// 通过js中this定义，this是运行中确定。方便“类”继承。

var parent = this;

var child;

// The constructor function for the new subclass is either defined by you

// (the "constructor" property in your `extend` definition), or defaulted

// by us to simply call the parent constructor.

// 如果protoProps属性中含有constructor及是一个构造函数，但是这里有不够安全。child即继承这个构造函数。

if (protoProps && _.has(protoProps, 'constructor')) {

  child = protoProps.constructor;

} else {

//否则继承this(父类的构造函数）

  child = function(){ return parent.apply(this, arguments); };

}

// Add static properties to the constructor function, if supplied.

//给子类增加静态属性（方法）

_.extend(child, parent, staticProps);

// Set the prototype chain to inherit from `parent`, without calling

// `parent`'s constructor function and add the prototype properties.

//创造一个空对象获取父类的原型对象和增加原型对象，赋值给子类的原型对象，丰富子类原型对象。

child.prototype = _.create(parent.prototype, protoProps);

// 调整子类constructor使其指向正确

child.prototype.constructor = child;

// Set a convenience property in case the parent's prototype is needed

// later.

// 方便子类调用父类原型对象上的方法

child.__super__ = parent.prototype;

// 返回子类

return child;

};

//创建一个Person“类”

var Person = function(name,age,job){

    this.name = name;

    this.age = age;

    this.job = job;

}

//Person.prototype原型对象

Person.prototype={

    sayName:function(){

        alert(this.name);

    },

    constructor:Person //重写constructor确保指向正确

};

//继承

var Man = function(name,age,job,sex){

    Person.apply(this,argument);//通过函数apply的方法使this.age,this.name,this.job中的this指向到Man实例化的对象中

    this.sex=sex;

}

//原型对象的继承

//方法一，这种方法重复构造函数一次

Man.prototype = new Person();

//方法二，创建一个空构造函数

var F = function(){};

F.prototype = new Person();

Man.prototype = new F();

Man.prototype.constructor = Man;