Code Exercise for JS Position - Magic Numbers

magicNumbers.js

/**
 * Method which takes a given, natural number and calculates
 * a series of magic numbers until a number repeats (returns false),
 * or equals 1 (returns true).
 *
 * EX: fn(1) === true // (1 equals 1)
 * EX: fn(7) === true // (7 -> 49 -> 97 -> 130 -> 10 -> 1)
 * EX: fn(11) === false // (11 -> 2 -> 4 -> 16 -> 37 -> 58 -> 89 -> 145 -> 42 -> 20 -> 4 [repeat]) 
 *
 * @param {number} x - given, natural number
 * @returns {boolean} whether the magic numbers repeat (false) OR return 1 (true)
 */
function magicNumbers(x) {
  const prevMagicNumbers = new Set();

  while (x !== 1) {
    prevMagicNumbers.add(x);
    
    x = String(x).split('').reduce((a, b) => a + b * b, 0);

    if (prevMagicNumbers.has(x)) return false;
  }

  return true;
}