JS/JavaScript编写倒计时程序

多的我就不写了  主要是核心代码 javascript : <script type="text/javascript"> var countdown = 60; function settime(val) { var stime = setTimeout( function() { settime(val) },1000 ) if (countdown == 0) { val.removeAttribute("disabled"); val.value = "发送验证码"; countdown = 60; clearTimeout(stime); } else { val.setAttribute("disabled", true); val.value = "重新发送(" + countdown + ")"; countdown--; } } </script>

html: <input type="button" id="btn" value="发送验证码" onclick="settime(this)">