js实现页面的秒数倒计时

<button name="vcode_mail" class="btn btn-default" type="button" id="vcode_mail-btn" onclick="vcode_mail_post(this)">免费获取验证码</button>

js

    //发送验证码
    function vcode_mail_post(obj){
        var seconds =;
 
        //获取邮箱
        var email = $("input[name='email']").val();
        //异步变同步
        /*$.ajaxSettings.async = false;*/
        //发送请求
        $.post("{:url('index/user/vcode_mail_post')}",{email:email,type:},function(data){
 
            var message = data.message;
            if(data.ok == ''){
                alert(message);
                //倒计时
                daojishi(seconds,obj);
            }else{
                alert(message);
 
            }
        },'json');
        /*$.ajaxSettings.async = true;*/
    }
 
    //倒计时
    function daojishi(seconds,obj){
 
        if (seconds > ){
 
                seconds--;
 
                $(obj).text(seconds+"秒后可重新获取 ").attr("disabled", true);//禁用按钮
 
                // 定时1秒调用一次
 
                setTimeout(function(){
 
                    daojishi(seconds,obj);
 
                },);
 
            }else{
 
                $(obj).text("重新获取验证码").attr("disabled", false);//启用按钮
 
            }
    }