●

index.html

<html>
<head>
<script type="text/javascript" src="move.js"></script>
</head>
<body>
<p>●</p>
</body>
</html>

move.js

var buru=2;
var posleft=100;
var postop=100;
function move(){
  obj=document.getElementsByTagName("p");
  for(i=0;i<obj.length;i++){
    obj[i].style.position="absolute";
    obj[i].style.left = posleft+"px";
    obj[i].style.top = postop+"px";
  }
  buru *=-1;
  posleft +=buru*Math.random();
  postop  +=buru*Math.random();
  setTimeout(move,100);
}
 var addListener =function(elm, type, func){
 if(! elm){return false;}
   if(elm.addEventListener){/*W3C*/
	elm.addEventListener(type, func, false);
   }else if(elm.attachEvent){/*Internet Explorer*/
 	elm.attachEvent('on'+type, func);
   }else{
	return false;
   }
   return true;
 };

addListener(window, "load", move);