JS写的计时器，把代码贴上，可以参考

js代码：

 var maxtime = 7;function CountDown(){ var tokenid = document.getElementById("tokenid");if(maxtime>=0){minutes = Math.floor(maxtime/60);seconds = Math.floor(maxtime%60);msg="剩余"+minutes+"分"+seconds+"秒";--maxtime;}else{clearInterval(timer);msg="重新生成";maxtime=7;tokenid.disabled=false;}  tokenid.value=msg;}function getToken(){ var tokenid1 = document.getElementById("tokenid"); var uid=document.getElementById("uid").value;  timer = setInterval("CountDown()",1000); tokenid1.disabled=true; } 

html代码：

<input type="button" id="tokenid" value="获取动态密码" style="width:85px;height:29px;valign:middle" onclick="getToken();"/>