Permutation with recursion

permutate.js

const insertItem = (xs, index, item) => [...xs.slice(0, index), item, ...xs.slice(index)];
const range = number => [...Array(number).keys()];
const permutate = (xs, accum = []) => {
  const [head, ...tail] = xs;

  if (!head) {
    return accum;
  }

  return accum.length === 0
    ? permutate(tail, [[head]])
    : permutate(
        tail,
        accum.reduce((tempAccum, arrayValue) => {
          const insertPositions = range(arrayValue.length + 1);
          const insertHeadIntoArray = insertItem(head)(arrayValue);
          return tempAccum.concat(insertPositions.map(insertHeadIntoArray));
        }, [])
      );
};

console.log(permutate([1, 2, 3]));
/*
[ [ 3, 2, 1 ],
  [ 2, 3, 1 ],
  [ 2, 1, 3 ],
  [ 3, 1, 2 ],
  [ 1, 3, 2 ],
  [ 1, 2, 3 ] ]
*/
console.log(permutate(['a', 'b', 'c']));
/*
[ [ 'c', 'b', 'a' ],
  [ 'b', 'c', 'a' ],
  [ 'b', 'a', 'c' ],
  [ 'c', 'a', 'b' ],
  [ 'a', 'c', 'b' ],
  [ 'a', 'b', 'c' ] ]
*/