js的拖拽事件的鼠标抬起元素仍然运动的问题

<div style = "position: absolute;left: 0;top: 0;"></div>
function addEvent(elem , type , handle) {
    if(elem.addEventListener) {
        elem.addEventListener(type , handle , false);
    }else if(elem.attachEvent) {
        elem.attachEvent('on' + type, function(){
            handle.call(elem);
        })
    }else{
        elem['on' + type] = handle;
    }
}

具体代码如下：
<script>  
    function drag(ele){
        var disX,
            disY;
        var move = function(e){
                    var event = e || window.event;
                    ele.style.left = e.pageX - disX + "px";
                    ele.style.top = e.pageY - disY + "px";
                }
        var up =  function () {
                    move = null;
                    alert (1)
                }    
        var down = function(e){
                    disX = e.pageX - parseInt(ele.style.left);
                    disY = e.pageY - parseInt(ele.style.top);
                    addEvent(document , 'mousemove' , move)
                    addEvent(document , 'mouseup' , up)
                } 
        addEvent(ele , 'mousedown' , down)        
    }
    var div = document.getElementsByTagName('div')[0];    
    drag(div)
</script>

js鼠标拖动事件_lirunhui6的博客-CSDN博客_js监听鼠标的移动事件第一步，定义被拖放的元素为绝对定位或者相对定位第二部，清楚几个坐标的概念：按下鼠标时指针坐标（event.pageX和event.pageY）,松开鼠标时指针坐标，拖放元素的原始坐标，拖放后元素的坐标<!doctype html><html><head><meta charset="utf-8"><title></title..

https://blog.csdn.net/lirunhui6/article/details/80055452

参考一下。说明没移除事件