Adding client side validation failures to ASP.NET MVC ModelState

Question

Within a HTTP post page I have the following DIV specified:

<div class="centered" style="text-align:center">
  <span class="help-block">
    @Html.ValidationSummary(true)
  </span>
</div>

I have the following javascript validation:

function validate() {

        var cardTypeCheck = RealexRemote.validateCardType(document.getElementById('cardType').value);
        var cardNumberCheck = RealexRemote.validateCardNumber(document.getElementById('cardNumber').value);
        var cardHolderNameCheck = RealexRemote.validateCardHolderName(document.getElementById('cardholderName').value);
        var expiryDateMonthCheck = RealexRemote.validateExpiryMonthDateFormat(document.getElementById('expiryDateMM').value);
        var expiryDateYearCheck = RealexRemote.validateExpiryYearDateFormat(document.getElementById('expiryDateYY').value);
        var expiryDateFormatCheck = RealexRemote.validateExpiryDateFormat(document.getElementById('expiryDateMM').value.concat(document.getElementById('expiryDateYY').value));
        var expiryDatePastCheck = RealexRemote.validateExpiryDateNotInPast(document.getElementById('expiryDateMM').value.concat(document.getElementById('expiryDateYY').value));
        if (document.getElementById('cardNumber').value.charAt(0) == "3") { cvnCheck = RealexRemote.validateAmexCvn(document.getElementById('cvn').value); }
        else { cvnCheck = RealexRemote.validateCvn(document.getElementById('cvn').value); }
        if (cardNumberCheck == false || cardHolderNameCheck == false || expiryDateYearCheck == false || expiryDateYearCheck == false || expiryDateFormatCheck == false || expiryDatePastCheck == false || cvnCheck == false) {
            // code here to inform the cardholder of an input error and prevent the form submitting
            if (cardTypeCheck == false) { alert("Card Type must be selected") }
            if (cardNumberCheck == false) { alert("Card Number entered is not valid") }
            if (expiryDateMonthCheck == false) { alert("Expiry Date Month must be selected") }
            if (expiryDateYearCheck == false) { alert("Expiry Date Year must be selected") }
            if (expiryDateMonthCheck == true && expiryDateYearCheck == true)
            {
                if (expiryDatePastCheck == false) { alert("Expiry Date must not be in the past") }
            }                
            if (cardHolderNameCheck == false) { alert("Card Holder name must be entered") }                
            if (cvnCheck == false) {  }
            return false;
        }
        else
            return true;
    }

Instead of putting out validation errors as javascript alerts I would like to add them to the ModelState Errors lists but I am unsure of how to do this when on the client side. I have attempted:

if (cvnCheck == false) {
  var ul = $(".help-block ul");
  ul.append("<li>Security Code must be entered</li>")
}

But this is not displaying, how can I set my ModelState to be invalid on the client side

Answer 1

var helpBlock = $(".help-block"); helpBlock.append("<div class=\"validation-summary-errors\"></div>");
$(".validation-summary-errors").append("<li>" + "Expiry Date Year must be selected" + "</li>");