Credit card checker (step 3)

Hi, I’m stuck at sub-step 2 of step 3… Credit card checker project.

I expected newArr of valid1 to be updated and printed to the console but 0 is printed instead.
What’s wrong with my code? Also, is there a way to see how the computer process my code (so that i know what went wrong in the process)?

Below is my code. Thanks for any help!

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

// Add your functions below:
let validateCred = (arr) => {
  let newArr = arr.slice(0).reverse();
  for (let i = 1; i < newArr.length; i += 2) {
      if (newArr[i] * 2 > 9) {
       newArr = newArr[i] * 2 - 9;
      } else if (newArr[i]*2 < 9) {
      } newArr = newArr[i] * 2;
    }   
   console.log(newArr)
  }
 
 validateCred(valid1)