Find all permutations for a specified string

all-permutations.js

/**
 * Traverse permutation to add new letter to every new position
 * 
 * @example
 * generateNextPermutation(['a','b'],'c')
 * // => [['c','a','b'],['a','c','b'],['a','b','c']]
 */
function generateNextPermutation(permutation, ch) {
  const destination = [];
  for (let i = 0; i <= permutation.length; i++) {
    const nextPermutation = permutation.slice();
    nextPermutation.splice(i, 0, ch);
    destination.push(nextPermutation);
  }
  return destination;
}

/**
 * Traverse over all permutations to add new letter to every new position in every permutation
 * 
 * @example
 * generateNextPermutations([['a','b'],['b','a']],'c')
 * // => generateNextPermutation(['a','b'],'c')
 * // => generateNextPermutation(['b','a'],'c')
 * // => [['c','a','b'],['a','c','b'],['a','b','c'],['c','b','a'],['b','c','a'],['b','a','c']]
 */
function generateNextPermutations(permutations, ch) {
    const nextPermutations = [];
    for (let j = 0; j < permutations.length; j++) {
      nextPermutations.push(...generateNextPermutation(permutations[j], ch));
    }
    return nextPermutations;
}

/**
 * Generate permutations for letters within the specified string
 * 
 * @example
 * perm('abc')
 * // => generateNextPermutations([['a']],'b')
 * // => generateNextPermutations([['a','b'],['b','a']],'c')
 * // => [['c','a','b'],['a','c','b'],['a','b','c'],['c','b','a'],['b','c','a'],['b','a','c']]
 */
function perms(str) {
  let permutations = [[str[0]]];
  for (let i = 1; i < str.length; i++) {
    permutations = generateNextPermutations(permutations, str[i]);
  }
  return permutations;
}