原生JS实现元素跟随鼠标拖动事件

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html:<div id='box' style="width:100px;height:100px;background-color:'#ee735c'">  <div>可拖动div元素</div></div>

JS:var oDiv=document.getElementById('box')  oDiv.onmousedown=function(ev){    var disX=ev.clientX-oDiv.offsetLeft    var disY=ev.clientY-oDiv.offsetTop    document.onmousemove=function(ev){      var l=ev.clientX-disX      var t=ev.clientY-disY      oDiv.style.left=l+'px'      oDiv.style.top=t+'px'    }    document.onmouseup=function(){      document.onmousemove=null;      document.onmouseup=null    }  }