Hi everyone, I am trying to work through the credit card challenge project and I am really not sure how to go about it, some guidance would be appreciated :’)

```
// Add your functions below:
function validateCred ()=> {};
validateCred.splice(-1, 1);
const digit=(1,3,5,7,9);
const newDigit=(digit-9);
for(let digit=0; digit< 13; --digit){
if(digit){
return digit * 2;
}
if (digit *2 > 9){
return newDigit;
}
if(newDigit + ????? % 10 === 0){
console.log('valid');
}else{
console.log('invalid');
}
}
```

link: https://www.codecademy.com/practice/projects/credit-card-checker

I am basically stuck at summing up all the numbers, your advice would be helpful