Generates combinations of strings within array of strings

stringListCombinations.js

// @flow

export const stringListCombinationsWithoutSort = (a: string[], transformer: (str: string) => string): string[] => {
  return a.reduce((accumulator, propName, i) => [
    propName,
    ...accumulator,
    ...(accumulator.map((s) => (s + (transformer ? transformer(propName) : propName)))),
  ], [])
}

export const stringListCombinations = (a: string[], transformer: (str: string) => string): string[] => {
  return a.reduce((accumulator, propName, i) => [
    ...accumulator,
    [propName],
    ...(accumulator.map((s) => ([...s, (transformer ? transformer(propName) : propName)]))),
  ], [])
  .sort((a, b) => a.length === b.length ? 0 : a.length > b.length ? 1 : -1)
  .map(a => a.join(''))
}

// const testArray = ['a', 'b', 'c', 'd']

// stringListCombinations(testArray, (s) => (s[0].toUpperCase() + s.slice(1)))
// ["a", "b", "c", "d", "aB", "aC", "bC", "aD", "bD", "cD", "aBC", "aBD", "aCD", "bCD", "aBCD"]

// stringListCombinationsWithoutSort(testArray, (s) => (s[0].toUpperCase() + s.slice(1)))
// ["a", "b", "c", "d", "aB", "aC", "bC", "aD", "bD", "cD", "aBC", "aBD", "aCD", "bCD", "aBCD"]