coding basics if / else and return (for example in javascript)

Question

I have been some time coding, not to much as you will see (1-2 years), but I am facing this question and I am feeling ashamed. This is not the first time I am confused about it. I have looked in some books of other languages as Java, but I can't solve it by myself.

Why in this script the return is undefined?

const factorial = n => {
  let result = 1;
  const rec = (n) => {
    if(n>0) {
    result = result * n;
    rec(n-1);
    } else {
    console.log(result)
    return result;
    }
  }
  return rec(n);
};

console.log(factorial(5))
120
undefined

PS: I edited to clear what I would like to understand. Why function rec is not returning result?

Answer 1

Your function has multiple calls. Either return from all of them, or none of them.

const factorial = n => {
  if(n>0) {
    return factorial(n-1) * n;
  } else {
    return 1;
  }
};


const factorial = n => {
  let result = 1;
  const rec = (n) => {
    if(n>0) {
      result = result * n;
      rec(n-1);
    }
  }
  rec(n);
  return result;
};

The alternative is to loop, not recurse

const factorial = n => {
  let result = 1;
  for (; n>0; n--) {
    result = result * n;
  }
  return result;
};