可拖拽div

      function dragFunc(id){
            var Drag = document.getElementById(id);
            console.log(Drag)
            Drag.onmousedown = function(event){//mousedown 事件。 与 click 事件不同，mousedown 事件仅需要按键被按下，而不需要松开即可发生
                console.log(event);
                var ev = event || window.event;
                event.stopPropagation();
                var disX = ev.clientX - Drag.offsetLeft;
                var disY = ev.clientY - Drag.offsetTop;
                document.onmousemove = function(event) {
                    var ev = event || window.event;
                    Drag.style.left = ev.clientX - disX + "px";
                    Drag.style.top = ev.clientY - disY + "px";
                    Drag.style.cursor = "move";
                };
            }
             Drag.onmouseup = function() {
                document.onmousemove = null;
                this.style.cursor = "default";
            };
        }
        dragFunc('box');