@inject IConfiguration cfg
@{
    var total = cfg.GetValue<int>("CaptchaSeconds");
    var sec = total;
    var session = this.Context.Session;
    var model = session.Get<CodeCaptchaModel>(CodeCaptchaModel.Key);
    if (model != null)
    {
        sec = (int)(model.ExpireDateUtc - DateTime.UtcNow).TotalSeconds;
    }
}
<script>
    var total = @total;
    var sec = @sec;
    var timer;
    function StartTimer(sec) {
        if (sec > 0) {
            $('#send-code').attr("disabled", "disabled").attr("value", "重发" + sec + "秒");
            timer = setTimeout('StartTimer("' + (sec - 1) + '")', 1000);
        }
        else {
            $('#send-code').removeAttr("disabled").attr("value", "发送验证码");
            EndTimer();
        }
    }
    function EndTimer() {
        clearTimeout(timer);
    }
    $(function () {
        if (sec > 0 && sec < total) {
            StartTimer(sec);
        }
    });
    $(function () {
        $('#send-code').click(function () {
            $(this).attr("disabled", "disabled");
            if (!valid()) {
                $(this).removeAttr("disabled");
                return;
            }
            var url = getUrl();
            $.getJSON(url, function (json) {
                if (json.success) {
                    StartTimer(json.data);
                }
                else {
                    alert(json.data);
                    $(this).removeAttr("disabled");
                }
            }).fail(function () {
                $(this).removeAttr("disabled")
            });
            return false;
        });
    });
</script>