PermutateString.js

'use strict'

const permutate = (aString) => {
 if (typeof aString !== 'string' || !aString) {
 throw new Error('The arg must be a valid, non empty string')
 }
 const characters = aString.split('')
 let permutations = [[characters.shift()]]
 while (characters.length) {
 const currentCharacter = characters.shift()
 permutations = calculateCurrentCharacterPermutation(
 permutations,
 currentCharacter
 )
 }
 return permutations
 .map((character) => character.join(''))
 .filter((item, index, self) => self.indexOf(item) === index)
 .sort()
}

const calculateCurrentCharacterPermutation = (
 allPermutations,
 currentCharacter
) => {
 const currentPermutations = []
 allPermutations.forEach((permutation) => {
 let index = 0
 while (index <= permutation.length) {
 const tmp = [...permutation]
 tmp.splice(index, 0, currentCharacter)
 currentPermutations.push(tmp)
 index++
 }
 })
 return currentPermutations
}

export { permutate }