js,JQ获取短信验证码倒计时

<a href="javasript:void(0);"onclick="settime(this);">获取手机验证码</a>

    <script>
        var countdown=60; 
        function settime(obj) { 
            if (countdown == 0) { 
                obj.getAttributeNode(‘onclick‘).value ="settime(this);";   
                obj.textContent="免费获取验证码"; 
                countdown = 60; 
                return;
            } else { 
                obj.getAttributeNode(‘onclick‘).value ="javascript:void(0);";
                obj.setAttribute("disabled", true); 
                obj.textContent="重新发送(" + countdown + ")"; 
                countdown--; 
            } 
        setTimeout(function() { 
            settime(obj) 
            },1000) 
        }
    </script>