A project of Codecademy in Java Script

Credit Card Checker

// 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:
//Copying the credit card number to copyCredNum, doubling every second digit from the end to the beginning
const validateCred = (credNum) => {
  let copyCredNum = credNum.slice();
  for (let i = copyCredNum.length - 2; i >= 0; i-=2) {
    copyCredNum[i] *= 2;
    if (copyCredNum[i] > 9) {
      copyCredNum[i] -= 9;
    }
  }
  //console.log(copyCredNum)
  //Checking if the sum of digits in a card is devided by 10 without a remainder = valid, else invalid 
  const sumCredNum = copyCredNum.reduce((a, b) => {
    return a + b});
    //console.log(sumCredNum);
    if (sumCredNum % 10 !== 0) {
      return "invalid";
        } else {
  return "valid"; 
}}
 // Calling the function for a single card above, in a function for a batch of cards, and saving a list of invalid cards:
 const findInvalidCards = credBatch => {
   let listInvalid = [];
        for (i = 0; i < credBatch.length; i++){
          if (validateCred(credBatch[i]) === "invalid") {
            listInvalid.push(credBatch[i]);
          }
  }
  return listInvalid;
   }
 console.log("List of invalid Cards Numbers:", findInvalidCards(batch));
 //Checking credCompanies that issued invalidCards. Iterating through the invalid card list, and according to first digit (indicating company), pushing those to an array.
 const idInvalidCardCompanies = listInvalid => {
   let credCompanies = [];
   let getInvalidCreds = findInvalidCards(listInvalid);

   //Push into an array the first digit of each invalid card, to then be checked against company names
   for (let i = 0; i < getInvalidCreds.length; i++) {
     let companyNums = getInvalidCreds[i].slice(0, 1);
     if (companyNums == 3) {
       credCompanies.push('Amex');
     } else if (companyNums == 4) {
       credCompanies.push('Visa'); 
     } else if (companyNums == 5) {
       credCompanies.push('Mastercard');
     } else if (companyNums == 6) {
       credCompanies.push('Discover'); 
   } else {
     return 'Company not found';
   }  
    }
     //To avoid duplicate reports of company name,  returning each name just once (using .includes())
    let companyShortList = [];
   if (credCompanies.includes('Amex') === true) {
     companyShortList.push('Amex');
   }
   if (credCompanies.includes('Visa') === true) {
     companyShortList.push('Visa');
     }
     if (credCompanies.includes('Mastercard') === true) {
     companyShortList.push('Mastercard');
     }
     if (credCompanies.includes('Discover') === true) {
       companyShortList.push('Discover');
  }
  return companyShortList;
 }

console.log(idInvalidCardCompanies(batch));



  

Codecademy project for checking credit card validity and reporting names of companies who issued invalid cards. There are 15 arrays that each contain the digits of separate credit card numbers. They are in variables that reflect their status: valid and mystery. There is also a batch array that stores all of the provided credit cards in a single array. These arrays are used to check if the code are working properly.

A function, validateCred() has a parameter of an array, representing a single credit card number. It returns "valid" when an array contains digits of a valid credit card number and "invalid" when it is invalid. This function does not mutate the values of the original array.

Luhn algorithm is used to check credit card validity. The calculations in the Luhn algorithm are broken down as the following steps: Iterating backwards - from the 2nd digit at the end to the beginning of a credit card number), every other digit is doubled . If the result is greater than 9 after doubling, subtracting 9 from the result. Summing up all the digits in the credit card number. If the sum modulo 10 is 0 (if the sum divided by 10 has a remainder of 0) then the number is valid, otherwise, it’s invalid.

The function findInvalidCards() checks a batch of cards (an array of arrays = a nested array) for which cards are invalid, and returns a nested array of the invalid cards. It calls the function validateCred() to check each card in the batch.

The credit card companies that have possibly issued invalid cards are identified. The function, idInvalidCardCompanies() has one parameter for a nested array of invalid numbers and returns an array of companies, according to their unique first digits. The following table shows which digit is unique to which company:

First Digit Company 3 Amex (American Express) 4 Visa 5 Mastercard 6 Discover If the number doesn’t start with any of the numbers listed, print out a message like: “Company not found”.

An array of the first digits is created, and then, to avoid duplicate reports of a company, each company appearing in that array will be reported only once.