Caesar cipher in JavaScript (ES6)

caesar-shift.js

/**
 * Applies a Caesar shift to all alphabetical characters in a string.
 * Characters are converted to uppercase in the returned string.
 * @param {int} key - Positions to shift (0-25).
 * @param {string} str - The string to shift.
 * @return {string} The shifted string.
 */
function caesarShift(str, key) {
  return str.toUpperCase().replace(/[A-Z]/g, c => String.fromCharCode((c.charCodeAt(0)-65+key)%26+65))
}