js获取验证码倒计时的实现方法

<script src="./js/jquery-1.8.3.min.js"></script> 
<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>