js ex

function validateCreditCard(creditCardNum){

  //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('9999-9999-8888-0000')); //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