js初级学习之拖拽功能 明天写分析

        div1.onmousedown = function(){
            var l = event.clientX - div1.offsetLeft;
            var t = event.clientY - div1.offsetTop;
            document.onmousemove = function(){
                var needX = event.clientX - l;
                var needY = event.clientY - t;
                if(needX<0){needX=0;}
                if(needY<0){needY=0;}
                //var w = screen.availWidth - div1.offsetWidth;
                //var h = screen.availHeight - div1.offsetHeight;
                var w = innerWidth - div1.offsetWidth;
                var h = innerHeight - div1.offsetHeight;
                if(needX>w){needX = w;}
                if(needY>h){needY = h;}
                div1.style.left = needX + 'px';
                div1.style.top = needY + 'px';
            }
            document.onmouseup = function(){
                //document.onmousedown = null;
                document.onmousemove = null;
                document.onmouseup = null;
            }
        }

**

• 功能说明 ID为div1 的div在body体中，可以被鼠标拖拽。

**