javascript function only returns undefined

Question

The following javascript function only returns undefined

function digital_root(n) {
  var x = String(n).split('');
  if (x.length > 1) {
    sum = x.reduce((accumulator, value) => parseInt(value) + accumulator, 0);
    digital_root(sum);
  } else {
    console.log(x);
    return x;
  }
}

however it prints the correct value when run in node. So why does it return undefined?

> digital_root(12)
[ '3' ]
undefined

If I take the console.log(x) statement out, the function still returns undefined

> digital_root(12)
undefined

@MarianTheisen You were correct, that was the issue. I didn't realize I needed a return statement there as well. — Timothy Pulliam
– Timothy Pulliam, Commented Apr 14, 2021 at 16:25

connexo · Accepted Answer · 2021-04-14 16:25:41Z

1

The first time your function runs it goes into the if block, where it calls itself again with argument digital_root(3).

This "inner" call is processed first now, this time going into the else block, where the console.log(x) call happens and then return ['3'] explicitly returns that value to the outer function call, so that return value is not shown on the console.

After the inner call returned the value, the outer function terminates, because there's nothing left to do, so the outer function never returns anything.

Functions do have a default return value of undefined whenever there is not explicit return statement.

edited Apr 14, 2021 at 16:25

answered Apr 14, 2021 at 16:16

connexo

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1 Comment

Timothy Pulliam Over a year ago

If I take the console.log(x) statement out, the function still only returns undefined. However, I know that x should be returned since it was able to printed. Or am I misunderstanding something fundamental?

Timothy Pulliam · Accepted Answer · 2021-04-14 16:23:43Z

0

I figured it out. I needed to include return for the recursive call.

The full code should look like this

function digital_root(n) {
  var x = String(n).split('');
  if (x.length > 1) {
    sum = x.reduce((accumulator, value) => parseInt(value) + accumulator, 0);
    return digital_root(sum);
  } else {
    console.log(x);
    return x;
  }
}

answered Apr 14, 2021 at 16:23

Timothy Pulliam

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