JS倒數計時

<input type="button" id="btn" value="免費獲取驗證碼" />
<script type="text/javascript">
var wait=60;
function time(o) {
		if (wait == 0) {
			o.removeAttribute("disabled");			
			o.value="免費獲取驗證碼";
			wait = 60;
		} else {
			o.setAttribute("disabled", true);
			o.value="重新傳送(" + wait + ")";
			wait--;
			setTimeout(function() {
				time(o)
			},
			1000)
		}
	}
document.getElementById("btn").onclick=function(){time(this);}
</script>