Auto Scope State to Selectors in Root Reducer

index.js

//reducers/index.js

import { scopeStateToSelectors } from '../helpers/redux'
import threads, { selectors as threadsSelectors } from './threads'

...

// Scopes the state sent down to each of the selector functions by the key:
export const selectors = scopeStateToSelectors({
  threads: threadsSelectors,
})


/* ---------- VS ---------- */

import threads, { selectors as threadsSelectors } from './threads'

export const getActiveThread = (state) => threadsSelectors.getActiveThread(state.threads)
export const getThreadByID = (state, id) => threadsSelectors.getThreadByID(state.threads, id)
...n

scopeStateToSelectors.js

// helpers/redux.js

import _ from 'lodash'

export const scopeStateToSelectors = (selectorsMap) => {
  return _.reduce(selectorsMap, (allScopedSelectors, selectors, scope) => (
    _.reduce(selectors, (scopedSelectors, selector, selectorName) => ({
      ...scopedSelectors,
      [selectorName]: (state, ...rest) => selector(state[scope], ...rest),
    }), allScopedSelectors)
  ), {})
}

threads.js

// reducers/threads.js

...

export const selectors = {
  getThreadByID: (state, id) => { // state comes in scoped down to state.threads
    return _.find(state.threads, { id })
  },
  getActiveThread: (state) => { // state comes in scoped down to state.threads
    return _.find(state.threads, { id: state.activeThreadID })
  },
  ...
}