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" />