1const permutations = arr => {
2  if (arr.length <= 2) return arr.length === 2 ? [arr, [arr[1], arr[0]]] : arr;
3  return arr.reduce(
4    (acc, item, i) =>
5      acc.concat(
6        permutations([...arr.slice(0, i), ...arr.slice(i + 1)]).map(val => [
7          item,
8          ...val,
9        ])
10      ),
11    []
12  );
13};