get-all-characters.js

const getAllCharacters = () => {
  let chars = '';

  for (let i = 0; i <= 0x10ffff; i++) {
    try {
      chars += String.fromCodePoint(i);
    } catch (e) {
      // ignore invalid utf-16 chars
      continue;
    }
  }

  return chars;
}

console.log(getAllCharacters().length)