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Caesar Cipher and ROT13 Text Shifting

Shift ASCII letters by any integer offset with alphabet wrapping, and expose ROT13 as a fixed thirteen-position special case.

JavascriptSecurity Boundaries

Code

snippet
function shiftLetters(text, offset) {
  if (typeof text !== "string") throw new TypeError("text must be a string");
  if (!Number.isInteger(offset)) throw new TypeError("offset must be an integer");
  const normalized = ((offset % 26) + 26) % 26;
  return text.replace(/[a-z]/gi, (char) => {
    const base = char <= "Z" ? 65 : 97;
    return String.fromCharCode(((char.charCodeAt(0) - base + normalized) % 26) + base);
  });
}

export function caesarCipher(text, offset) {
  return shiftLetters(text, offset);
}

export function rot13(text) {
  return shiftLetters(text, 13);
}

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