Caesar cipher

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!'

Caesar cipher

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