JavaScript面向对象实现拖拽与继承示例

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<style>
#div1 {width:100px; height:100px; background:red; position:absolute;}
#div2 {width:100px; height:100px; background:yellow; position:absolute;}
</style>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<script>
window.onload=function(){
  new Drag("div1");
  new Drag("div2");
}
function Drag(id)
{
  var _this=this;
  this.oDiv=document.getElementById(id);
  this.disX=0;
  this.disY=0;
  this.oDiv.onmousedown=function(ev){
    _this.fnDown(ev);
    return false;
  };
}
  Drag.prototype.fnDown=function(ev)
  {
    var _this=this;
    var oEvent=ev||event;
    this.disX=oEvent.clientX-this.oDiv.offsetLeft;
    this.disY=oEvent.clientY-this.oDiv.offsetTop;
    document.onmousemove=function(ev){
      _this.fnMove(ev);
    };
    document.onmouseup=function(){
      _this.fnUp();
    };
  };
  Drag.prototype.fnMove=function(ev)
  {
    var oEvent=ev||event;
    var l=oEvent.clientX-this.disX;
    var t=oEvent.clientY-this.disY;
    if(l<0)
    {
      l=0;
    }
    else if(l>document.documentElement.clientWidth-this.oDiv.offsetWidth)
    {
      l=document.documentElement.clientWidth-this.oDiv.offsetWidth;
    }
    if(t<0)
    {
      t=0;
    }
    else if(t>document.documentElement.clientHeight-this.oDiv.offsetHeight)
    {
      t=document.documentElement.clientHeight-this.oDiv.offsetHeight;
    }
    this.oDiv.style.left=l+'px';
    this.oDiv.style.top=t+'px';
  };
  Drag.prototype.fnUp=function()
  {
    document.onmousemove=null;
    document.onmouseup=null;
  };
</script>
</head>
<body>
<div id="div1"></div>
<div id="div2"></div>
</body>
</html>

function LimitDrag(id){
  Drag.call(this,id); //继承属性
}
for(var i in Drag.prototype){
  LimitDrag.prototype[i]=Drag.prototype[i];
}