html
<input type="button" onclick="settime(this)" value="免费获取验证码">
js
var countdown=60;
function settime(obj){
if(countdown==0){
obj.removeAttribute("disabled");
obj.value="免费获取验证码";
countdown=60;
return;
}
else{
obj.setAttribute("disabled",true);
obj.value="重新发送("+countdown+")";
countdown--;
}
setTimeout(function(){
settime(obj)},1000)
}