拖拽效果

var odiv = document.getElementById("box");
            var disX = 0;
            var disY = 0;
            odiv.onmousedown = function(ev){
                var ev = ev || window.event;
                disX = ev.clientX -odiv.offsetLeft;
                disY = ev.clientY -odiv.offsetTop;
                document.onmousemove = function(ev){
                    var ev = ev || window.event;
                    odiv.style.left = ev.clientX - disX + 'px';
                    odiv.style.top = ev.clientY - disY + 'px';
                }
                document.onmouseup = function(){
                    document.onmousemove = null;
                    document.onmouseup = null;
                }
            }