Factorialize a number by Porphyrogennitos


E.g. I write 5 and when I press the convert, it shows NaN. My JavaScript looks correct but for some reason, I get this error. I even tried the parseFloat around the document.getElementById("input").value but it didn’t fix the problem.

when you multiply by undefined you get NaN

It is because I’ve used arrow function?

no, look at your multiplication, what are the values in there?

num * convert(num - 1) but I don’t see something wrong. num is the document.getElementById("input").value so why is undefined?

num is fine
what’s the value of convert(num - 1)?

Well that’s the undefined but why? I copy pasted the recursion from the exercice. It should work.

If you look at the code example on the hint page you are missing the return. Have the convert function return a value and use that to set the textContent.

Also .value is a string, not a number and even though it will work I would suggest you implicitly convert it instead.

const convert = (num) => {
  if (num === 0) {
    return 1;
  } else {
    return num * convert(num - 1);

document.getElementById("convert").onclick = () => {
  document.getElementById("output").textContent = convert(
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