间隔时间显示数字html代码

<pre id="aa"></pre>

<div style="display:none" id="w">1,2,3,4,5,6,7 </div>

<input type="button" value="显示2" onclick="type1()" />

<script language="javascript">

var index=0; var word=document.getElementById("w").innerHTML; var set ;

function type1(){

set = setInterval(function(){

document.getElementById("aa").innerHTML = word.substring(0,index++);

if(index > 19){ clearInterval(set); }

}, 500); }

</script>