I literally have no clue what the credit card checker project is asking me to do

Web Development
1

As per this response on the above post by mirja_t…

" A common and simple approach would be this:

  1. Write a function (leave the body empty for now) that has a parameter for the card array
  2. In the function body copy the array in order to leave the input array unaltered (e.g. slice() method as mentioned in another post or spread syntax )
  3. Reverse the copied array in order to iterate from end to start (reverse() method)
  4. Write a new variable and assign it to an empty array
  5. Write a for loop that iterates over each digit in the copied and reversed array
  6. Inside the for loop, find out which index is odd (because that omits the check digit)
  7. If the index is odd, double the digit (if statement)
  8. If the result is larger than 10, subtract 9 (same, if statement)
  9. Push the result to the new array – also the unaltered digits from the even indexes of the for loop
  10. Sum up each digit from the new array (reduce() method or another loop)
  11. Find out if there is a rest if you divide the sum by 10 (modulo operator)
  12. Return true from the function is there is no rest value. "

Before reading post I found that my code happened to be following these steps. I have since gone in a different direction but I just wanted to know how I could succeed if I persevered in my original route. I mainly had problem with step 6. It was iterating through the wrong numbers. What are your tips for step 6 in particular?
Thanks.

2

To check whether i is even, you could do something like
(i % 2 === 1)
which would be true when i is odd, and would be false when i is even

3

Thanks for responses so far. Oops. I forgot to include my code. I hadn’t changed the sum to reduce yet. But good to know if I was going along the right lines as per the steps detailed above or whether I was way off. I may have been taking the copy, pop then reverse process literally instead of the more elegant way in the solution.

const validateCred = arr => {
let checkCard = […arr];
console.log(checkCard);
endDigit = checkCard.pop();
console.log(endDigit);
console.log(checkCard);
let reverseCard = checkCard.reverse();
console.log(reverseCard);
let numbers = ;
let dbl = 0;
for (let i = 0; i < reverseCard.length; i++) {
let n = reverseCard[i];
if (n % 2 !== 0) {
dbl = n *= 2;
if (dbl > 9) {
numbers.push(dbl -= 9);
} else {
numbers.push(n);
}
} else {
numbers.push(n);
}
console.log(numbers);
}
let sum = 0;
for (let a = 0; a < numbers.length; a++) {
sum += numbers[a];
}
if ((sum + endDigit) % 10 === 0) {
return true;
} else {
return false;
}
}

4

Most of it looks fine. But check the inside of the first for-loop.

I think you should have i % 2 instead of n % 2 to check if the index is odd or even, instead of if the number [at that index] is odd or even.
and you don’t need the *= and -= in situations where you don’t intend to change the value of the variable.

    if (i % 2 !== 0) {
      dbl = n * 2;
      if (dbl > 9) {
        numbers.push(dbl - 9);

You’re missing a let or const in front of the first endDigit, otherwise you’re modifying a global variable.