Caesar cipher

Isabelle Viktoria Maciohsek · JavaScript, Algorithm, String · Dec 29, 2020

Encrypts or decrypts a given string using the Caesar cipher.

  • Use the modulo (%) operator and the ternary operator (?) to calculate the correct encryption/decryption key.
  • Use the spread operator (...) and Array.prototype.map() to iterate over the letters of the given string.
  • Use String.prototype.charCodeAt() and String.fromCharCode() to convert each letter appropriately, ignoring special characters, spaces etc.
  • Use Array.prototype.join() to combine all the letters into a string.
  • Pass true to the last parameter, decrypt, to decrypt an encrypted string.
const caesarCipher = (str, shift, decrypt = false) => {
  const s = decrypt ? (26 - shift) % 26 : shift;
  const n = s > 0 ? s : 26 + (s % 26);
  return [...str]
    .map((l, i) => {
      const c = str.charCodeAt(i);
      if (c >= 65 && c <= 90)
        return String.fromCharCode(((c - 65 + n) % 26) + 65);
      if (c >= 97 && c <= 122)
        return String.fromCharCode(((c - 97 + n) % 26) + 97);
      return l;
    })
    .join('');
};
caesarCipher('Hello World!', -3); // 'Ebiil Tloia!'
caesarCipher('Ebiil Tloia!', 23, true); // 'Hello World!'

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