define-selectors

define-selectors is a solution to this stackoverflow problem. It works based on Reselect and Re-reselect.

Installation

$ npm install define-selectors

Comparison with reselect

reselect:

import { createSelector } from 'reselect'
const inputSelector1 = (state) => state.val1
const inputSelector2 = (state) => state.val2

const someSelector = createSelector([
  inputSelector1,
  inputSelector2,
], ( val1, val2 ) => {
  // expensive calculation
  return val1 + val2
})

define-selectors:

import defineSelectors from 'define-selectors'
const inputSelector1 = (state) => state.val1
const inputSelector2 = (state) => state.val2

const { someSelector } = defineSelectors({
  someSelector: [[
    inputSelector1,
    inputSelector2,
  ], ( val1, val2 ) => {
    // expensive calculation
    return val1 + val2
  }],
})

// equivalent to above
const { someSelector } = defineSelectors({
  someSelector: {
    inputSelectors: [
      inputSelector1,
      inputSelector2,
    ],
    resultFunc: ( val1, val2 ) => {
      // expensive calculation
      return val1 + val2
    },
  },
})

Usage

import defineSelectors from 'define-selectors'

const selectNav = state => state.nav
const selectPage = state => state.page
const selectFoo = state => state.foo

const { selectNavAndPageAndFoo, selectNavAndPage } = defineSelectors({

  selectNavAndPageAndFoo: [
    [ 'selectNavAndPage', selectFoo ],      // Note! 'selectNavAndPage' must be string type!
    (navAndPage, foo) => {
      return `${navAndPage}/${foo}`
    },
  ],

  selectNavAndPage: [
    [ selectNav, selectPage ],
    (nav, page) => {
      return `${nav}/${page}`
    },
  ],
})

const state = { nav: 'navA', page: 'pageB', foo: 'fooC' }
console.log( selectNavAndPageAndFoo(state) )    // 'navA/pageB/fooC'

API

define-reselect consists in just one method exported as default.

import defineSelectors from 'define-reselect'

defineSelectors( selectors )

• selectors is a object. key: selectorName, value: selectorData pairs

{
  selectorName1: selectorData1,
  selectorName2: selectorData2,
  ...
}

• selectorData is a very important here. it is a object or array. selectorData contains inputSelectors, resultFunc, resolverFunc, cacheSize, customSelectorCreator. inputSelectors, resultFunc are required and the remainings are optional.

• selectorData(array):

[ inputSelectors, resultFunc, resolverFunc, cacheSize, customSelectorCreator ]

Note these index position. If you want to use customSelectorCreator but don't want resolverFunc and cacheSize try this:

[ inputSelectors, resultFunc, void 0, void 0, customSelectorCreator ]

• selectorData(object)

{
  inputSelectors: inputSelectors,
  resultFunc: resultFunc,
  resolverFunc: resolverFunc,
  cacheSize: cacheSize,
  customSelectorCreator: customSelectorCreator,
}

• inputSelectors(array): refer Reselect project. To avoid difinition ordering problem, you have to define each selector in the same selectors object. When you use the selector in the same selectors as inputSelector, use selectorName as the string type. In above example, when selectNavAndPageAndFoo is defined, it recursively go to the selectNavAndPage selector to define this first. FOUND_CIRCULAR_REFERENCE error occurs if a circular reference is found.
• resultFunc(function): refer Reselect project
• resolverFunc(function): refer Re-reselect project
• cacheSize(number): refer my unmerged PR to reselect
• customSelectorCreator(function): refer Reselect project

Contributing

Happy to PR any of the improvements you're thinking about. Thanks!