div 随机移动

<div id="ad" style="position:absolute;width=100;height=80">
<a href="#" target="_blank">
<img src="ad.jpg" border="0" width=100 height=90>
</a></div>
  <script>
  var x = 50,y = 60
  var xin = true, yin = true
  var step = 1   //这里设置移动步长，越小每次移动越短
  var delay = 10   //这里设置移动速度，越小越快
  var obj=document.getElementById("ad")
  function floatAD() {
     var L=T=0
     var R= document.body.clientWidth-obj.offsetWidth
     var B = document.body.clientHeight-obj.offsetHeight
     obj.style.left = x + document.body.scrollLeft
     obj.style.top = y + document.body.scrollTop
     x = x + step*(xin?1:-1) 
     if (x < L) { xin = true; x = L}
     if (x > R){ xin = false; x = R}
     y = y + step*(yin?1:-1)
     if (y < T) { yin = true; y = T }
     if (y > B) { yin = false; y = B }
  }
  var itl= setInterval("floatAD()", delay)
obj.onmouseover=function(){clearInterval(itl)}
obj.onmouseout=function(){itl=setInterval("floatAD()", delay)}
  </script>