how to return a string in js with al lower case and capital in upper case code example

Example: captitalize js

function capitalize2(str) {
  str = str.toLowerCase();

  const arrOfWords = str.split(" ");

  const arrOfWordsCased = [];

  for (let i = 0; i < arrOfWords.length; i++) {
    const char = arrOfWords[i].split("");
    char[0] = char[0].toUpperCase();

    res.push(char.join(""));
  }
  return arrOfWordsCased.join(" ");
}