recursion - Javascript recursive function not returning value?

Question

Im solving a codewars problem and im pretty sure i've got it working:

function digital_root(n) {
    // ...
    n = n.toString();
    if (n.length === 1) {
        return parseInt(n);
    } else {
        let count = 0;
        for (let i = 0; i < n.length; i++) {
            //console.log(parseInt(n[i]))
            count += parseInt(n[i]);
        }
        //console.log(count);
        digital_root(count);
    }
}

console.log(digital_root(942));

Essentially it's supposed to find a "digital root":

A digital root is the recursive sum of all the digits in a number. Given n, take the sum of the digits of n. If that value has two digits, continue reducing in this way until a single-digit number is produced. This is only applicable to the natural numbers.

So im actually getting the correct answer at the end but for whatever reason on the if statement (which im watching the debugger run and it does enter that statement it will say the return value is the correct value.

But then it jumps out of the if statement and tries to return from the main digital_root function?

Why is this? shouldn't it break out of this when it hits the if statement? Im confused why it attempt to jump out of the if statement and then try to return nothing from digital_root so the return value ends up being undefined?

Answer 1

You're not returning anything inside else. It should be:

return digital_root(count);
^^^^^^^

Why?

digital_root is supposed to return something. If we call it with a one digit number, then the if section is executed, and since we return from that if, everything works fine. But if we provide a number composed of more than one digit then the else section get executed. Now, in the else section we calculate the digital_root of the count but we don't use that value (the value that should be returned). The line above could be split into two lines of code that makes it easy to understand:

var result = digital_root(count); // get the digital root of count (may or may not call digital_root while calculating it, it's not owr concern)
return result;                    // return the result of that so it can be used from the caller of digital_root