1，继承

2，子类继承父类时，不继承父类的私有属性
代码如下:
/**
* @param {String} className
* @param {String/Function} superCls
* @param {Function} classImp
*/
function $class(className, superCls, classImp){
if(superCls === '') superCls = Object;
function clazz(){
if(typeof this.init == "function"){
this.init.apply(this, arguments);
}
}
var p = clazz.prototype = new superCls();
var _super = superCls.prototype;
window[className] = clazz;
classImp.apply(p, [_super]);
}

先写个父类
代码如下:
/**
* 父类 Person
*/
$class('Person','',function(){
// 私有属性age
var age;
this.init = function(n, a){
// 公有属性name
this.name = n;
// 私有属性初始化
age = a;
};
this.getName = function(){
return this.name;
};
this.setName = function(name){
this.name = name;
}
this.getAge = function(){
return age;
};
this.setAge = function(a){
age = a;
};
});

写子类，继承于Person
代码如下:
$class("Man",Person, function(supr){
var school;
this.init = function(n, a, s){
supr.init.apply(this, [n,a]);
school = s;
}
this.getSchool = function(){
return school;
};
this.setSchool = function(s){
school = s;
};
});

new一个子类实例
代码如下:
var m = new Man('tom', 25, 'pku');
console.log(m.name); // tom 继承父类的共有属性name可以直接使用点操作符获取
console.log(m.age); // undefined 父类的私有属性age不能直接使用点操作符获取
console.log(m.getAge()); // 25 可通过父类的共有方法getAge获取私有属性age
console.log(m.school); // undefined Man自己的私有属性仍然不能通过点操作符获取
console.log(m.getSchool()); // pku 通过getSchool()方法获取私有属性school