js 10秒倒計時 功能

請等待<span id="dd">10</span>秒
<script type="text/javascript">
function run(){
 var s = document.getElementById("dd");
 if(s.innerHTML == 0){
  window.location.href='regform.shtml';
  return false;
 }
 s.innerHTML = s.innerHTML * 1 - 1;
}
window.setInterval("run();", 1000);
</script>