<script>
var A = function ()
{
    this.alert = function ()
    {
        alert('A');
    }
}

var B = function ()
{
    this.alert = function ()
    {
        alert('B');
    }
}
var A = new A();
var B = new B();

A.alert();
</script>

<script>
Aspects = new Object();
Aspects.addBefore = function(obj, fname, before) {
    var oldFunc = obj[fname];
    obj[fname] = function() {
        return oldFunc.apply(this, before(arguments, oldFunc, this));
    };
};
Aspects.addAfter = function(obj, fname, after) {
    var oldFunc = obj[fname];
    obj[fname] = function() {
        return after(oldFunc.apply(this, arguments), arguments, oldFunc, this);
    };
};
Aspects.addAround = function(obj, fname, around) {
    var oldFunc = obj[fname];
    obj[fname] = function() {
        return around(arguments, oldFunc, this);
    };
};



var A = function (){
    this.alert = function (){
        alert('A');
    }
}

var B = function (){
    this.alert = function (){
        alert('B');
    }
}
var a = new A();
var b = new B();

Aspects.addAfter(a,"alert",b.alert);//将b.alert方法动态增加给a

a.alert();


</script>

------解决方案--------------------
楼主找找 js 继承

写一个类，继承A

------解决方案--------------------

方法1

var A=function()
{
   B.apply(this,arguments);
   this.alert = function ()
   {
       alert('A');
   }
}

var B=function()
{
   this.alert = function ()
   {
       alert('B');
   }
}

这种方法缺点是A函数把B函数里的同名方法覆盖了

方法2

var A=function()
{
   this.alert = function ()
   {
       alert('A');
   }
}

var B=function()
{
   this.alert = function ()
   {
       alert('B');
   }
}
A.prototype=new B();

new A().alert();
A.prototype.alert.apply();


方法3
var A=function()
{
   this.alert = function ()
   {
       alert('A');
   }
}

var B=function()
{
   this.alert = function ()
   {
       alert('B');
   }
}
function c(){
 var a=new A();
  var b=new B();
 a.alert();
 b.alert();
}
var s=new c();

------解决方案--------------------
不必要那样复杂。
JScript code

<script>
Function.prototype.$Asynch = function ( Method ) {
    this ();
    Method ();
}

var A = function ()
{
    this.alert = function ()
    {
        alert('A');
    }
}

var B = function ()
{
    this.alert = function ()
    {
        alert('B');
    }
}

var A = new A();
var B = new B();
A.alert.$Asynch( B.alert )
</script>

------解决方案--------------------
JS继承

------解决方案--------------------

JScript code
            var A = function ()
            {
                this.alert = function ()
                {
                    alert('A');
                }
            }
            var B = function ()
            {
                this.alert = function ()
                {
                    a