Missing Letter: return undefined

How to return undefined in a function in JS.
return undefined; statement does not work

Thanks for your answer P1xt. I didn’t check like that. I just asked something like returnUndefined() without the var output and I got a blank screen, though it works with return anything other than undefined (number, string, null, false, true).

Still i don’t understand why my code ( see here https://repl.it/CiBf/9) doesn’t pass the missing letter test. I will try to use some built-in function to loop over my array but would like very any clue about my code.

:disappointed:; completly stupid I am, thanks a lot. Even this afternoon, i remembered that return undefined works fine as i commented the for loop and tested it !!