js 验证码 倒计时60秒

                            **js 验证码 倒计时60秒**

<input type="button" id="btn" value="免费获取验证码" />  <script type="text/javascript">  var wait=60;  function time(o) {          if (wait == 0) {              o.removeAttribute("disabled");                        o.value="免费获取验证码";              wait = 60;          } else {              o.setAttribute("disabled", true);              o.value="重新发送(" + wait + ")";              wait--;              setTimeout(function() {                  time(o)              },              1000)          }      }  document.getElementById("btn").onclick=function(){time(this);}  </script>