ts/js short Heap's algorithm for strings permutation

permu.ts

  const permutations = (combo: string[]): string[][] => {
    // combo[]
    return combo
      .map((v, i, combo) => {
        const right = [...combo]
        const left = right.splice(i, 1)[0] // remove and return index from array;
        if (right.length === 0) {
          return [[left]]
        }

        return permutations(right).map((right) => [left, ...right])
      })
      .reduce((p: string[][], c) => p.concat(c))
  }