用javascript实现多张图片的交替展现

<script language=javascript>
var numAD=0;
var imgAD = new Array();//存储图片的src地址为数组。
imgAD[0] = "images/change/1.gif";
imgAD[1] = "images/change/2.gif";
imgAD[2] = "images/change/3.gif";
imgAD[3] = "images/change/4.gif";
function setTransition(){
  if(document.all){
    u.filters.revealTrans.Transition=Math.floor(Math.random()*23);
    u.filters.revealTrans.apply();
  }
}
function playTransition(){
  if(document.all){
    u.filters.revealTrans.play();
  }
}
function nextAD(){
  setTransition();
  document.u.src=imgAD[numAD];
  playTransition();
  if(numAD >= imgAD.length-1){
    numAD=0;
  }else{
    numAD++;
  }
  setTimeout("nextAD()",5000);
}
</script>

 <img src="images/change/1.gif"  width="452" height="231"  name="u" id="u" style="FILTER: revealTrans(duration=2,transition=20)"  >

 <script language="JavaScript">nextAD()</script>