capitalizeFirstString.js

word = "hello world what is up?";

function capitalize(words) {
  let word = words.split(" ");
  let capital = [];
  for (i = 0; i < word.length; i++) {
    capital.push(word[i].charAt(0).toUpperCase() + word[i].slice(1));
  }
  return capital.join(" ");
}

console.log(capitalize(word));