Factorialize a number by Porphyrogennitos

JavaScript
1

CodePen.

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.

2

when you multiply by undefined you get NaN

3

It is because I’ve used arrow function?

4

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

5

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

6

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

7

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

8

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.

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

document.getElementById("convert").onclick = () => {
  document.getElementById("output").textContent = convert(
    Number(document.getElementById("input").value)
  );
};
1 Like
9

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