Credit Card Challenge in Javascript Syntax Part 2 does not return valid on all valid cards

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#1

I’m new to studying Javascript and I’ve just got stuck on this project. My code only shows some of the valid numbers as valid.

// Add your functions below:
const validateCred = array => {
  const newArr = array.reverse();
  let check = newArr.shift();
  let doubledSum = 0;
  let singleSum = 0;
  for (let i=1; i<newArr.length; i+= 2) {
    if ((newArr[i]*2) > 9){
      doubledSum += ((newArr[i]*2)-9);
    } else {
    doubledSum += newArr[i]*2;
    }
  }
  for (let j =0; j< newArr.length; j+=2) {
    singleSum += newArr[j];
    
  }
  const result = (singleSum + doubledSum + check) % 10; 
  if (result === 0) {
    console.log('valid');
  } else {
    console.log('invalid');
  }

  
}
validateCred([5, 5, 3, 5, 7, 6, 6, 7, 6, 8, 7, 5, 1, 4, 3, 9]);
// This is supposed to be a valid card number but it is logging invalid to the console.type or paste code here

[https://www.codecademy.com/paths/full-stack-engineer-career-path/tracks/fscp-22-javascript-syntax-part-ii/modules/wdcp-22-credit-card-checker/projects/credit-card-checker]

#2

Hi,
a few observations:

This causes the original array (credit card number) to be reversed because it doesn’t make a copy of the array. That will cause trouble when you will continue with the other functions to follow.

Same thing here: It will alter the original array passed into the function.

Since you stripped the check digit from the array, and if I remember correctly, you should double every other digit starting with the number right next to the check digit, this for loop should start at 0 and the other one should start at 1 instead.

So if you swap the starting numbers of the two for loops and make a real copy of the array like this for example:

const newArr = [...array];
newArr.reverse();

You should be done with the 1st function.

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#3

Thank you! I can see now where I was wrong. Now it works out like it should.

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