Challenge Project: Credit Card Checker | Feedback appreciated

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Hi Everyone,

This is my first time posting anything on Codecademy Forums.
Is there anything that I may improve on this code? I hope you share your thoughts on my code.

// 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];

// Array of 4 accepted companies which each have unique first digits assigned.
const companies = [
    {firstDigit: 3, cName: 'Amex (American Express)'}, 
    {firstDigit: 4, cName: 'Visa'}, 
    {firstDigit: 5, cName: 'Mastercard'}, 
    {firstDigit: 6, cName: 'Discover'}
];

//console.log(companies[2].cName);

//----------------------------------------------------------------------------\\

const validateCred = arr => {

    let lastIndexNumber = arr.length-1;
    let sumOfEvens = 0;
    let sumOfOdds = 0;
    //Sums of Even digits and Odd digits of the selected array(arr)

    if (lastIndexNumber % 2 === 0) {
        for (let i = lastIndexNumber; i >= 0; i--) {
            if (i % 2 === 0)    {sumOfEvens += arr[i];
            } 
            else {
                if (arr[i] < 5) {sumOfOdds += arr[i]*2;} 
                else {sumOfOdds += arr[i]*2-9}
            }
        } 
    }

    else {     
        for (let j = lastIndexNumber; j >= 0; j--) {
            if (j % 2 === 1){
                sumOfOdds += arr[j];
            }       
            else {
                if (arr[j] < 5) {sumOfEvens += arr[j]*2;} 
                else {sumOfEvens += arr[j]*2-9}
            }
        }
    }
        
    let sumOfEvensAndOdds = sumOfEvens + sumOfOdds;    
    //Luhn algoritmasını test edebilmek üzere rakamların toplandığı değişken.

    if (sumOfEvensAndOdds % 10 === 0)
        {return true;}
    else 
        {return false;}

};

//console.log(validateCred(valid3));


const findInvalidCards = arr => {
    let invalidCardsDeck = [];
    
    for(let i = 0; i < arr.length; i++) {
        if(validateCred(arr[i]) === false){
            invalidCardsDeck.push(arr[i]);
        }                      
    } 
    return invalidCardsDeck;
};
    
//console.log(findInvalidCards(batch));

const invalidCardCompanies = arr => {
    let invalidCards = findInvalidCards(arr);
    let listOfInvalidCompanies = [];
    
    for(let i = 0; i < invalidCards.length; i++) {

        for(let j = 0; j < companies.length; j++){
            if (invalidCards[i][0] === companies[j].firstDigit){
                listOfInvalidCompanies.push(companies[j].cName);
            }
        }
    }

    let uniqueList = [...new Set(listOfInvalidCompanies)];

    return uniqueList;

};

//console.log(invalidCardCompanies(batch));

Thank you,
ZeePLA.