Shuffle array

shuffle.js

/**
 * Randomise array order
 * @param {Array} arr Array to randomise
 * @param {Object} [options]
 * @param {Boolean} [options.mutate] Sets if should modify given array. Defaults to false
 * @param {Function} [options.rand] Randomly generate an integer j: min <= j < max
 * @returns {Array}
 */
const shuffle = (arr, options) => {
  const len = arr.length;
  const { rand, mutate } = {
    rand: (min, max) => Math.floor(Math.random() * (max - min) + min),
    mutate: false,
    ...options,
  };
  const list = mutate ? arr : [...arr];
  for (let i = 0; i < len; ++i) {
    const j = rand(i, len);
    [list[i], list[j]] = [list[j], list[i]];
  }
  return list;
};

// https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle

// See also
// - https://github.com/pazguille/shuffle-array/blob/master/index.js