<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
<script type="text/javascript">
var a;
var value = 25;
window.onload = function() {
//2s执行一次
a = setInterval(count, 2000);
}
function count() {
document.getElementById("div1").innerHTML = value;
value = value - 1;
if (value <= 20)
clearInterval(a);
}
</script>