为什么我的信用卡验证不起作用?

我正在给表单添加一个信用卡验证。

如果用户点击注册按钮，有一个无效的信用卡号码，那么将有一个错误标记，标签将变成红色。

它还确保CVV字段和邮政编码字段不是空的。

现在，如果我在字段为空时单击按钮，我会根据需要得到错误。

如果我然后填写邮政编码和CSV并再次单击注册，那么错误将被删除。

没有删除CC号标志。

为什么会这样，我该如何修复它?

代码如下，谢谢:

// Form validation. Display error messages and don't let the user submit the form if any of these validation errors exist:
document.querySelector("button").addEventListener("click", function(e) {
    //check there's a valid credit card number
    var ccNum = document.getElementById("cc-num");
    var ccNumLbl = document.getElementById("cc-numLbl");

// takes the form field value and returns true on valid number
//algorithm found here: https://gist.github.com/DiegoSalazar/4075533
function valid_credit_card(value) {
  // accept only digits, dashes or spaces
    if (/[^0-9-'s]+/.test(value)) return false;
    // The Luhn Algorithm. It's so pretty.
    var nCheck = 0, nDigit = 0, bEven = false;
    value = value.replace(/'D/g, "");
    for (var n = value.length - 1; n >= 0; n--) {
        var cDigit = value.charAt(n),
              nDigit = parseInt(cDigit, 10);
        if (bEven) {
            if ((nDigit *= 2) > 9) nDigit -= 9;
        }
        nCheck += nDigit;
        bEven = !bEven;
    }
    return (nCheck % 10) == 0;
}

    if(!valid_credit_card(ccNum.input)) {
        ccNumLbl.style.color = "red";
        e.preventDefault();
    } else {
        ccNumLbl.style.color = "black";
    }
    //check there's a zip code
    var zip = document.getElementById("zip");
    var zipLbl = document.getElementById("zipLbl");
    if(zip.value.length === 0) {
        zipLbl.style.color = "red";
        e.preventDefault();
    } else {
        zipLbl.style.color = "black";
    }
    //check there's a cvv
    var cvv = document.getElementById("cvv");
    var cvvLbl = document.getElementById("cvvLbl");
    if(cvv.value.length === 0) {
        cvvLbl.style.color = "red";
        e.preventDefault();
    } else {
        cvvLbl.style.color = "black";
    }
});

和html:

<div id="credit-card" class="credit-card">
  <div class="col-6 col">
    <label id="cc-numLbl" for="cc-num">Card Number:</label>
    <input id="cc-num" name="user_cc-num" type="text">
  </div>
  <div class="col-3 col">
    <label for="zip" id="zipLbl">Zip Code:</label>
    <input id="zip" name="user_zip" type="text"> 
  </div>
  <div class="col-3 col">
    <label id="cvvLbl" for="cvv">CVV:</label>
    <input id="cvv" name="user_cvv" type="text"> 
  </div>
  <label>Expiration Date:</label>
  <select id="exp-month" name="user_exp-month">
    <option value="1">1 - January</option>
    <option value="2">2 - February</option>
    <option value="3">3 - March</option>
    <option value="4">4 - April</option>
    <option value="5">5 - May</option>
    <option value="6">6 - June</option>
    <option value="7">7 - July</option>
    <option value="8">8 - August</option>
    <option value="9">9 - September</option>
    <option value="10">10 - October</option>
    <option value="11">11 - November</option> 
    <option value="12">12 - December</option>                       
  </select>  
  <select id="exp-year" name="user_exp-year">
    <option value="2016">2016</option>
    <option value="2017">2017</option>
    <option value="2018">2018</option>
    <option value="2019">2019</option>
    <option value="2020">2020</option>                      
  </select>                                
</div>
<button type="submit">Register</button>