What will be the output of the following recursive function?

function countVowels(str) {
  if (str === "") {
    return 0;
  }
  let firstChar = str.charAt(0).toLowerCase();
  let remainingStr = str.substr(1);
  if (firstChar === "a" || firstChar === "e" || firstChar === "i" || firstChar === "o" || firstChar === "u") {
    return 1 + countVowels(remainingStr);
  }
  return countVowels(remainingStr);
}
console.log(countVowels("Hello World"));