solution to the credit card checker project

main.js

// All valid credit card numbers
const valid1 = [4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8];
const valid2 = [5, 5, 3, 5, 7, 6, 6, 7, 6, 8, 7, 5, 1, 4, 3, 9];
const valid3 = [3, 7, 1, 6, 1, 2, 0, 1, 9, 9, 8, 5, 2, 3, 6];
const valid4 = [6, 0, 1, 1, 1, 4, 4, 3, 4, 0, 6, 8, 2, 9, 0, 5];
const valid5 = [4, 5, 3, 9, 4, 0, 4, 9, 6, 7, 8, 6, 9, 6, 6, 6];

// All invalid credit card numbers
const invalid1 = [4, 5, 3, 2, 7, 7, 8, 7, 7, 1, 0, 9, 1, 7, 9, 5];
const invalid2 = [5, 7, 9, 5, 5, 9, 3, 3, 9, 2, 1, 3, 4, 6, 4, 3];
const invalid3 = [3, 7, 5, 7, 9, 6, 0, 8, 4, 4, 5, 9, 9, 1, 4];
const invalid4 = [6, 0, 1, 1, 1, 2, 7, 9, 6, 1, 7, 7, 7, 9, 3, 5];
const invalid5 = [5, 3, 8, 2, 0, 1, 9, 7, 7, 2, 8, 8, 3, 8, 5, 4];

// Can be either valid or invalid
const mystery1 = [3, 4, 4, 8, 0, 1, 9, 6, 8, 3, 0, 5, 4, 1, 4];
const mystery2 = [5, 4, 6, 6, 1, 0, 0, 8, 6, 1, 6, 2, 0, 2, 3, 9];
const mystery3 = [6, 0, 1, 1, 3, 7, 7, 0, 2, 0, 9, 6, 2, 6, 5, 6, 2, 0, 3];
const mystery4 = [4, 9, 2, 9, 8, 7, 7, 1, 6, 9, 2, 1, 7, 0, 9, 3];
const mystery5 = [4, 9, 1, 3, 5, 4, 0, 4, 6, 3, 0, 7, 2, 5, 2, 3];

// An array of all the arrays above
const batch = [valid1, valid2, valid3, valid4, valid5, invalid1, invalid2, invalid3, invalid4, invalid5, mystery1, mystery2, mystery3, mystery4, mystery5];


// Add your functions below:
let validateCred = array => {
  let even_odd = true;
  let double_array = [];
  let sum = 0;
  let double_num;
  for (let i=array.length-1; i>=0; i-- ) {
    if(even_odd) {
      sum += array[i]
      even_odd = false;
    } else {
      double_num = array[i]*2;
      if (double_num > 9){
        double_num -= 9;
      }
      double_array.push(double_num);
      sum += double_num;
      even_odd = true;
    }
  }
  if (sum % 10 == 0) {
    return true;
  } else {
    return false;
  }
};


const findInvalidCards = nestedArray => {
  let invalidCards = [];
  for ( let i=0; i<nestedArray.length; i++) {
    if (!(validateCred(nestedArray[i]))) {
      invalidCards.push(nestedArray[i]);
    }
  }
  return invalidCards;
};

let idInvalidCardCompanies = invalidCards => {
  let invalidCardCompanies = [];
  let amex = true;
  let visa = true;
  let master = true;
  let discover = true;
  for (let i=0; i<invalidCards.length; i++) {
    if(!(amex || visa || master || discover)) {
      break;
    }
    if(invalidCards[i][0] == 3 && amex) {
      invalidCardCompanies.push("Amex");
      amex = false;
    } else if (invalidCards[i][0] == 4 && visa) {
      invalidCardCompanies.push("Visa");
      visa = false;
    } else if (invalidCards[i][0] == 5 && master) {
      invalidCardCompanies.push("Mastercard");
      master = false;
    } else if (invalidCards[i][0] == 6 && discover) {
      invalidCardCompanies.push("Discover");
      discover = false;
    }
  }
  return invalidCardCompanies;
}

console.log(idInvalidCardCompanies(findInvalidCards(batch)));