学步园

       //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).