Using composition on a Store

collection.js

export const unique = (values) => [ ...new Set(values) ]

export const add = (value, position = 'first') => (values) => {
  return position === 'first'
    ? [ value, ...values ]
    : [ ...values, value ]
}

compose.js

export default (...λs) => (value) => λs.reduce((value, λ) => λ(value), value)

options.js

import * as collection from './collection'
import compose from './compose'

export const DEFAULT_OPTION = {
  label: 'Todos',
  value: undefined
}

export const toOption = (value) => ({
  value,
  label: value
})

export const toOptions = (default_option = DEFAULT_OPTION) => compose(
  collection.unique,
  (items) => items.map(toOption),
  collection.add({ ...DEFAULT_OPTION, ...default_option }, 'first')
)

store-addresses.js

import compose from './compose'
import { toOptions } from './options'
import * as types from './types'

export const state = {
  addresses: [
    {
      city: 'São Paulo',
      state: 'São Paulo'
    },
    {
      city: 'Jundiaí',
      state: 'São Paulo'
    }
  ]
}

const getCities = compose(
  (addresses) => addresses.map(address => address.city),
  toOptions({ label: 'Todos' })
)

const getStates = compose(
  (addresses) => addresses.map(address => address.state),
  toOptions({ label: 'Todos' })
)

export const getters = {
  [types.ADDRESSES_CITIES]: ({ addresses }) => getCities(addresses),
  [types.ADDRESSES_STATES]: ({ addresses }) => getStates(addresses)
}