credit card input validation using regular expression in javascript

Question

I've been trying to get this done but no success. I am using regular expression to validate the credit card number entered by user based on the type of credit card selected through the radio button. But I keed having the alert for the all if statement. It looks like all the if else statements are tested.

There is the HTML code fragment: 

<code>
<p><b>Payment Information:</b></p>
         <fieldset>
            <input type="radio" name="payment" value="Visa" id="visa" />Visa &nbsp;
            <input type="radio" name="payment" value="Master Card" />Master Card &nbsp;
            <input type="radio" name="payment" value="American Express" />American Express &nbsp;
            <input type="radio" name="payment" value="Discover" />Discover <br /><br />
            <label>Card Number:</label>
            <input type="text" name="cardNumber" id="cardNum" size="30" value="" onblur="ValidateCreditCardNumber()" />
</code>



And there is my javascript function :

<code>

function ValidateCreditCardNumber(){

    var ccNum = document.getElementById("cardNum").value;



    var visaRegEx = /^(?:4[0-9]{12}(?:[0-9]{3})?)$/;
    var mastercardRegEx = /^(?:5[1-5][0-9]{14})$/;
    var amexpRegEx = /^(?:3[47][0-9]{13})$/;
    var discovRegEx = /^(?:6(?:011|5[0-9][0-9])[0-9]{12})$/; 


    if (visaRegEx.test(ccNum) === false ){ // Visa validation
       alert("Please provide a valid Visa number!");   
        }  
      else  
        {  
         alert("Thank You!");  
        }  

    if (mastercardRegEx.test(ccNum) === false){ // MasterCard validation
        alert("Please provide a valid MasterCard number!");  
        }  
      else  
        {  
        alert("Thank You!");  
        } 

    if(amexpRegEx.test(ccNum) === false){ // Amex  validation
        alert("Not a valid America Express number!");  
        }  
      else  
        {   
        alert("Thank You!");  
        } 

    if (discovRegEx.test(ccNum) === false){ // Discover validation
        alert("Please provide a valid Discover number!"); 
        }  
      else  
        {  
        alert("Thank You!");  
        } 


    }
</code>


Any kind of help or advice would be really appreciated.

Answer 1

Change your logic to this:

<script type="text/javascript">

// Store the regexes as globals so they're cached and not re-parsed on every call:
var visaPattern = /^(?:4[0-9]{12}(?:[0-9]{3})?)$/;
var mastPattern = /^(?:5[1-5][0-9]{14})$/;
var amexPattern = /^(?:3[47][0-9]{13})$/;
var discPattern = /^(?:6(?:011|5[0-9][0-9])[0-9]{12})$/; 

function validateCreditCardNumber() {

    var ccNum  = document.getElementById("cardNum").value;

    var isVisa = visaPattern.test( ccNum ) === true;
    var isMast = mastPattern.test( ccNum ) === true;
    var isAmex = amexPattern.test( ccNum ) === true;
    var isDisc = discPattern.test( ccNum ) === true;

    if( isVisa || isMast || isAmex || isDisc ) {
        // at least one regex matches, so the card number is valid.

        if( isVisa ) {
            // Visa-specific logic goes here
        }
        else if( isMast ) {
             // Mastercard-specific logic goes here
        }
        else if( isAmex ) {
            // AMEX-specific logic goes here
        }
        else if( isDisc ) {
            // Discover-specific logic goes here
        }
    }
    else {
        alert("Please enter a valid card number.");
    }
}

</script>

Answer 2

You have 4 different if blocks in your case, which hits every single block when the previous once fail.

Replace if with if else, that way if will only validate for a single use case. Also you need not let the user know to be specific about the type of card that he is trying to enter. Just a single message to enter a valid number should suffice.

function ValidateCreditCardNumber() {

  var ccNum = document.getElementById("cardNum").value;
  var visaRegEx = /^(?:4[0-9]{12}(?:[0-9]{3})?)$/;
  var mastercardRegEx = /^(?:5[1-5][0-9]{14})$/;
  var amexpRegEx = /^(?:3[47][0-9]{13})$/;
  var discovRegEx = /^(?:6(?:011|5[0-9][0-9])[0-9]{12})$/;
  var isValid = false;

  if (visaRegEx.test(ccNum)) {
    isValid = true;
  } else if(mastercardRegEx.test(ccNum)) {
    isValid = true;
  } else if(amexpRegEx.test(ccNum)) {
    isValid = true;
  } else if(discovRegEx.test(ccNum)) {
    isValid = true;
  }

  if(isValid) {
     alert("Thank You!");
  } else {
     alert("Please provide a valid Visa number!");
  }
}