createPaginator.js

const createPaginator = (endpoint, resultKey) {

  const requestPage = (page) => ({
    type: 'REQUEST_PAGE',
    payload: {
      page
    },
    meta: {
      endpoint,
      resultKey
    }
  })

  const receivePage = (page, results) => ({
    type: 'RECEIVE_PAGE',
    payload: {
      page,
      results
    }
  })

  const pages = pages = {}, action = {}) => {

    switch (action.type) {
      case 'REQUEST_PAGE':
        return {
          ...pages,
          [action.payload.page]: {
            ids: [],
            fetching: true
          }
        }
      case 'RECEIVE_PAGE':
        return {
          ...pages,
          [action.payload.page]: {
            ids: action.payload.results.filter(item => item.id),
            fetching: false
          }
        }
      default:
        return pages
    }

  }

  const currentPage = (currentPage = 1, action = {}) =>
    action.type == ‘REQUEST_PAGE’ ? action.payload.page : currentPage

  const onlyForEndpoint = (reducer) => (state = {}, action = {}) =>
    typeof action.meta == ‘undefined’ ? state : action.meta.endpoint == endpoint ? reducer(state, action) : state

  const itemsReducer = (items = {}, action = {}) {
    switch (action.type) {
      case 'RECEIVE_PAGE':
        let _items = {}
        for (let item of action.payload.results) {
          _items = {
            ..._items,
            [item.id]: item
          }
        }
        return {
          ...items,
          ..._items
        }
      default:
        return items
    }
  }

  const reducer = onlyForEndpoint(
    combineReducers({
      pages,
      currentPage
    })
  )

  return {
    requestPage,
    receivePage,
    reducer,
    itemsReducer: onlyForEndpoint(itemsReducer)
  }

}

22 const pages = pages = {}, action = {}) => {

const pages = (pages = {}, action = {}) => {