为什么用document.body会出bug呢

<!DOCTYPE html>




<br> div{<br> height: 100px;<br> width: 100px;<br> background-color: red;<br> position: absolute;<br> }<br>



<br> var div1=document.getElementById(&quot;div1&quot;);<br> div1.addEventListener(&quot;mousedown&quot;,getDiv,false)<br> div1.addEventListener(&quot;mouseup&quot;,delDiv,false)<br> // document.body.addEventListener(&quot;mousemove&quot;,move,false);<br> function getDiv(){<br> var oevent=window.event||arguments[0];<br> div1.style.cursor=&quot;move&quot;;<br> document.addEventListener(&quot;mousemove&quot;,move,false);<br> // div1.style.left=oevent.clientX;<br> // div1.style.top=oevent.clientY;<br> }<br> function move(){<br> var oevent=window.event||arguments[0];<br> div1.style.left=oevent.clientX-50+&quot;px&quot;;<br> div1.style.top=oevent.clientY-50+&quot;px&quot;;<br> }<br> function delDiv(){<br> div1.style.cursor=&quot;auto&quot;;<br> var oevent=window.event||arguments[0];<br> div1.style.left=oevent.clientX-50+&quot;px&quot;;<br> div1.style.top=oevent.clientY-50+&quot;px&quot;;<br> document.removeEventListener(&quot;mousemove&quot;,move,false);<br> }<br>


这段代码中为什么用document.body.addEventListener("mousemove",move,false);添加事件在鼠标快速移动时会出现bug