Random-Thing/generateRandomString.js

function generateRandomString(length, ...modes) { // generateRandomString(99, 1, 2, 3, 4, 5)
  const modeCharacters = [
    '0123456789', // Mode 1
    'abcdefghijklmnopqrstuvwxyz', // Mode 2
    'ABCDEFGHIJKLMNOPQRSTUVWXYZ', // Mode 3
    '!@#$%^&*()-_=+[]{}|;:\'",<.>/?`~\\', // Mode 4
  ];
  // ABot
  const unicodeCharacters = (() => {
    let result = '';
    const characterList = '1234567890ABCDEF';

    try {
      for (let i = 0; i < length; i++) {
        let chars = '';
        for (let j = 0; j < 4; j++) {
          chars += characterList[Math.floor(Math.random() * characterList.length)];
        }
        result += JSON.parse(`"\\u${chars}"`);
      }
    } catch (e) {
      console.error(e.stack);
      return '';
    }

    return result;
  })();

  modeCharacters.push(unicodeCharacters);

  let characters = '';

  modes.forEach(mode => {
    if (mode >= 1 && mode <= 5) {
      characters += modeCharacters[mode - 1];
    }
  });

  if (characters.length === 0) {
    return '';
  }

  let result = '';
  const charactersLength = characters.length;

  for (let i = 0; i < length; i++) {
    result += characters.charAt(Math.floor(Math.random() * charactersLength));
  }

  return result;
}