Credit Card Checker - function returning undefined

My code below is returning undefined after every section, first when I do the iteration to the left etc up until the sum, and then secondly after the sum. Please help!! Here’s a link to the project: Credit Card Checker Link

``````// 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];

const validateCred = array => {
for (var i = array.length - 2; i >= 0; i -= 2) {
array[i] = (array[i] * 2 % 9)
}
if (array[i] > 9) {
array[i] - 9
}  else {
array[i] = array[i]
/*return array[i];*/
}
const add = (a, b) => {
a + b
}
return sum

if ((sum / 10) === 0) {
return valid
} else {
return invalid
}

}
console.log(validateCred(valid1));

``````

Double check this arrow function that you use with the `.reduce()` method:

In an arrow function, when you include the curly braces `{ }`, you have to explicitly use the `return` keyword for it to return a value. Without that, it will be `undefined` like a regular function without a `return`.

When you don’t include the curly braces, then the result is returned by default.

To be clear, these two would both return the results of adding `a` and `b`:

``````const add = (a, b) => a + b;
// and
const add = (a, b) => {
return a + b;
}
``````

This won’t return anything, so JavaScript will use `undefined`:

``````const add = (a, b) => {
a + b
}
``````
1 Like

Thank you! Now, I’ve changed that its returning invalid when I’ve put in a valid array.

I’ve also taken out `return sum` which returned 80 when it was left in.

I think, further, that I need to return something after the first `if` statement but I can’t figure out what! (EDIT I returned the `array[i} - 9`

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