javascript的继承

       //对鼠标坐标点,进行封装的类        function PointXY(x, y) {            this.PointX = x;            this.PointY = y;        };        //重载一下pointXY的类构造函数        function PointXYOverLoad(client) {            this.Base = PointXY;            this.Base(client.clientX, client.clientY);        }

这样,PointXYOverLoad的一个实例,也就具有了PointX,PointY的属性(这2个属性是基类提供的).