js验证码，倒计时60秒

<input type="button" id="hysymd" style="margin:10px 0px 0px 10px;" value="获取验证码" class="btn" "hqyzm()"/>
<script type="text/javascript">
	 var countdown = 60;
	 function hqyzdl(){
		 if (countdown == 0) {
	    	 $("#hysymd").removeAttr("disabled");
	    	 $("#hysymd").val("获取验证码");
	         countdown = 60;
	     } else {
	    	$("#hysymd").attr("disabled", true)
	        $("#hysymd").val("重新发送(" + countdown + ")");
	    	countdown--;
	        setTimeout(function() {
	        	hqyzdl();
	        },1000)
	    }
	  }
  </script>