js读秒

<p class="authenticationFailure-p" id="reg_btn">上传成功，请稍后.... (0)</p>

<script>

        var wait_time = 4; //设置秒数(单位秒)
        var secs_time = 0;         
        for(var i=1;i<=wait_time;i++) {
            window.setTimeout("sTimer("+i+")",i*1000);
      }

    function sTimer(num) {
          var wait_time = 4; //设置秒数(单位秒)
           if(num==wait_time) {
                 window.location.href="../index.html";
           } else {
                 secs_time=wait_time-num;
                 document.getElementById("reg_btn").innerHTML="上传成功，请稍后.... ("+secs_time+")";
           }
     }

</script>