判断鼠标是否在对象上

    function isMouseInBox(obj)
    {  
        var oEvent = event || window.event;
        var point1 = new Array(event.clientX + document.body.scrollLeft, event.clientY + document.body.scrollTop);  
        var point2 = getObjPosition(obj);  
        
        return ((point1[0] >= point2[0]) && point1[1] >= point2[1] 
                                         && point1[0] - point2[0] <= obj.offsetWidth 
                                         && point1[1] - point2[1] <= obj.offsetHeight);
    }  

    function getObjPosition(obj)
    {  
        var point = new Array(0,0);  
        
        while (obj != document.body)
        {
            point[0] += obj.offsetLeft;
            point[1] += obj.offsetTop;
            obj = obj.offsetParent;
        }
        
        return point;
    }