js倒计时60秒获取验证码

			var wait=60;
			function settime(o) {
			        if (wait == 0) {
			            o.removeAttribute("disabled");
			            o.value="发送验证码";
			            wait = 60;
			        } else {
			            o.setAttribute("disabled", true);
			            o.value="重新发送(" + wait + ")";
			            wait--;
			            setTimeout(function() {
			                settime(o)
			            },
			            1000)
			        }
			    }

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