JavaScript实现鼠标拖拽框选效果完整代码

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" 
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>鼠标框选效果</title>
<style>
  *{
  padding:0;
  margin:0;
  }
  #bottom{
  position:absolute;
  bottom:0px;
  width:100%;
  height:40px;
  border:1px solid #000;
  background:#000;
  color:#fff;
  }
  .tempDiv{
  border:1px dashed blue;
  background:#5a72f8;
  position:absolute;
  width:0;
  height:0;
  filter:alpha(opacity:10);
  opacity:0.1
  }
</style>
<script type = "text/javascript">
  window.onload = function(){
  var stateBar = document.getElementById("bottom");
  document.onmousedown = function(e){
   var posx = e.clientX;
   var posy = e.clientY;
   var div = document.createElement("div");
   div.className = "tempDiv";
   div.style.left = e.clientX+"px";
   div.style.top = e.clientY+"px";
   document.body.appendChild(div);
   document.onmousemove = function(ev){
    div.style.left = Math.min(ev.clientX, posx) + "px";
    div.style.top = Math.min(ev.clientY, posy) + "px";
    div.style.width = Math.abs(posx - ev.clientX)+"px";
    div.style.height = Math.abs(posy - ev.clientY)+"px";
    stateBar.innerHTML = "MouseX: " + ev.clientX + "<br/>MouseY: " + ev.clientY;
    document.onmouseup = function(){
     div.parentNode.removeChild(div);
     document.onmousemove = null;
     document.onmouseup = null;
    }
   }
  }
}
</script>
</head>
<body>
   <div id = "bottom"></div>
</body>
</html>