JavaScript实现页面元素拖拽功能详解

<html>
 <head>
  <meta charset="utf-8">
  <style type="text/css">
  *{
   margin:0px;
   padding:0px;
  }
 #zhuantou{
  width:120px;
  height:60px;
  background-image:url(1.jpg);
  position:fixed;
  left:100px;
   top:50px;
  }
  </style>
 <body>
  <div id="zhuantou">
  </div>
  <script>
  var zt=document.querySelector("#zhuantou");
  var isPressed=false;
  var offsetX=0;
  var offsetY=0;
  zt.onmousedown=function(event){
     isPressed=true;
     this.style.cursor="move";
     offsetX=event.offsetX;
    offsetY=event.offsetY;
  };
  zt.onmouseup=function(){
    isPressed=false;
    this.style.cursor="default";
  };
  zt.onmousemove=function(event){
   if(!isPressed){
     return;
    }
   zt.style.left=(event.clientX-offsetX)+"px";
   zt.style.top=(event.clientY-offsetX)+"px";
  };
 </script>
 </body>
</html>