Homework: Credit Card Validation

You're starting your own credit card business. You need to come up with a new way to validate credit cards with a simple function called validateCreditCard that returns true or false.

Here are the rules for a valid number:

• Number must be 16 digits, all of them must be numbers
• You must have at least two different digits represented (all of the digits cannot be the same)
• The final digit must be even
• The sum of all the digits must be greater than 16

The following credit card numbers are valid:

• 9999777788880000
• 6666666666661666

The following credit card numbers are invalid:

• a92332119c011112 invalid characters
• 4444444444444444 only one type of number
• 1111111111111110 sum less than 16
• 6666666666666661 odd final number

In order to run the function, you'll need to know how to load javascript on an HTML page. From there, you will open your developer console to call the function.

function validateCreditCard(creditCardNum){

  // The credit card number must be 16 digits in length
  if(creditCardNum.length !== 16){
    return false;
  }

  // All of the digits must be numbers
  for(var i = 0; i < creditCardNum.length; i++){
    // store the current digit
    var currentNumber = creditCardNum[i];

    // turn the digit from a string to an integer (if the digit is in fact a digit and not anther char)
    currentNumber = Number.parseInt(currentNumber);

    // check that the digit is a number
    if(!Number.isInteger(currentNumber)){
      return false;
    }
  }

  // The credit card number must be composed of at least two different digits (i.e. all of the digits cannot be the same)
  var obj = {};
  for(var i = 0; i < creditCardNum.length; i++){
    obj[creditCardNum[i]] = true;
  }
  if(Object.keys(obj).length < 2){
    return false;
  }

  // The final digit of the credit card number must be even
  if(creditCardNum[creditCardNum.length - 1] % 2 !== 0){
    return false;
  }

  // The sum of all the digits must be greater than 16
  var sum = 0;
  for(var i = 0; i < creditCardNum.length; i++){
    sum += Number(creditCardNum[i]);
  }
  if(sum <= 16){
    return false;
  }

  return true;
};

/**** tests *****/
console.log(validateCreditCard('9999777788880000')); //true
console.log(validateCreditCard('6666666666661666')); //true
console.log(validateCreditCard('a92332119c011112')); //false
console.log(validateCreditCard('4444444444444444')); //false
console.log(validateCreditCard('1211111111111112')); //true

Bonus #1: A valid credit card number may also contain dashes, to make a card number easier to read. For example, the following credit card numbers are now also valid:

• 9999-7777-8888-0000
• 6666-6666-6666-1666

function validateCreditCard(ccNumberNoDashes) {

    //Remove dashes from creditCardNum string
    var ccNumberNoDashes = '';
    for (var i = 0; i < creditCardNum.length; i++) {
        if (creditCardNum[i] !== '-') {
            ccNumberNoDashes += creditCardNum[i];
        }
    }

    // The credit card number must be 16 digits in length
    if (ccNumberNoDashes.length !== 16) {
        return false;
    }

    // All of the digits must be numbers
    for (var i = 0; i < ccNumberNoDashes.length; i++) {
        // store the current digit
        var currentNumber = ccNumberNoDashes[i];

        // turn the digit from a string to an integer (if the digit is in fact a digit and not anther char)
        currentNumber = Number.parseInt(currentNumber);

        // check that the digit is a number
        if (!Number.isInteger(currentNumber)) {
            return false;
        }
    }

    // The credit card number must be composed of at least two different digits (i.e. all of the digits cannot be the same)
    var obj = {};
    for (var i = 0; i < ccNumberNoDashes.length; i++) {
        obj[ccNumberNoDashes[i]] = true;
    }
    if (Object.keys(obj).length < 2) {
        return false;
    }

    // The final digit of the credit card number must be even
    if (ccNumberNoDashes[ccNumberNoDashes.length - 1] % 2 !== 0) {
        return false;
    }

    // The sum of all the digits must be greater than 16
    var sum = 0;
    for (var i = 0; i < ccNumberNoDashes.length; i++) {
        sum += Number(ccNumberNoDashes[i]);
    }
    if (sum <= 16) {
        return false;
    }

    return true;
};

/**** tests *****/
console.log(validateCreditCard('9999-7777-8888-0000')); //true
console.log(validateCreditCard('6666-6666-6666-1666')); //true
console.log(validateCreditCard('a923-3211-9c01-1112')); //false
console.log(validateCreditCard('4444-4444-4444-4444')); //false
console.log(validateCreditCard('1211-1111-1111-1112')); //true

Bonus #2: Return an object indicating whether the credit card is valid, and if not, what the error is
{ valid: true, number: 'a923-3211-9c01-1112' }
{ valid: false, number: 'a923-3211-9c01-1112', error: ‘wrong_length’ }

Bonus #3: Make your credit card scheme even more advanced! What are the rules, and what are some numbers that pass or fail? Ideas: check expiration date! Check out the Luhn Algorithm for inspiration.