Here's the Luhn algorithm that takes an array of 16 digits to verify a valid credit card

luhnAlgorithm.js

const validateWithLuhn = (digits) => {
  //console.log("digits are: ", digits);
  let result = false;

  if (/^\d{16}$/.test(digits.join("")) == false) {
    //console.log('should be 16 hence false');
    return false;
  }

  const step = 2;
  let cummulative = 0;

  for( i=15; i >= 0; i--) {

    if (i % 2 == 0) {
      //console.log('luhn: ', digits[i]);

      const luhnValue = digits[i] * 2;

      if (luhnValue > 9) {
        cummulative += luhnValue - 9;
      } else {
        cummulative += luhnValue;
      }

    } else {
      //console.log('not luhn: ', digits[i])
      cummulative += digits[i];
    }
  }

  //console.log('Cummulative: ', cummulative);
  if (cummulative % 10 == 0) {
    result = true;
  }

  //console.log("Result: ", result);
  return result;

}