redux-scope

Redux Scope 🔭

Reduce Redux boilerplate and improve modularity.

Redux Scope logically brings together actions, action types, reducers and selectors by associating it with a redux scope. It provides helpers for creating actions and selectors which take care of creating unique action types and keep selectors wired correctly as you refactor your modules.

Installation

npm install redux-scope

Usage

Most of the apps are written as a collection of modules where each module has its own redux logic. Let's say we are writing a module taking care of user preferences, called preferences:

src/modules/preferences/redux.js

import { createScope, createAction, createSelector } from 'redux-scope';

export const setFontSize = createAction('set-font-size');

function reducer(state = { fontSize: 'small' }, action) {
  switch (action.type) {
    case setFontSize.type:
      return {
        ...state,
        fontSize: action.payload,
      };
    default:
      return state;
  }
}

export const fontSizeSelector = createSelector(state => state.fontSize);

export const preferencesScope = createScope('preferences', reducer, {
  setFontSize,
  fontSizeSelector,
});

src/app.js

import { createStore } from 'redux';
import thunk from 'redux-thunk';
import { createRootReducer } from 'redux-scope';
import {
  preferencesScope,
  setFontSize,
  fontSizeSelector,
} from 'src/modules/preferences';

const rootReducer = createRootReducer({
  preferencesScope,
  // other scopes go here
});

const store = createStore(rootReducer, applyMiddleware(thunk));

// use redux as usual
store.dispatch(setFontSize('big'));
const fontSize = fontSizeSelector(store.getState()); // 'big'

Redux Scope Lifecycle

Usually, Redux lifecycle can be separated into several phases:

1. all reducers are imported from their modules and combined together into a root reducer using combineReducers,
2. init action is fired to produce initial state,
3. store is ready for dispatching actions and reading from state.

But before that, in order for modules to cooperate well:

• action types are predefined and prefixed with module paths (or other unique identifier),
• every selector is defined to point to a correct place in resulting global state.

Redux Scope uses this separation between composing redux logic from different modules (Step 1) and actually using that logic (Step 3) to lazy evaluate action types and correct paths for selectors, so that you don't need to hardcode them inside modules.

Here is how Redux lifecycle looks with Redux Scope:

1. actions, selectors and reducer are added to a scope using createScope
2. all scopes are imported from their modules and combined together using combineScopes
3. root reducer is produced from scopes using createRootReducer, which also initializes all action types and selectors to correct values
4. init action is fired to produce initial state
5. store is ready for dispatching actions and reading from state

You don't have to think about action types, they will be prefixed automatically. When you write selectors with createSelector you only write how to select a property inside that module (state => state.fontSize), Redux Scope takes care of the rest.

Creating Thunks

src/modules/user/redux.js

import { createThunk, createScope } from 'redux-scope';
import { fetchUserDataAsync } from './my-user-api';

export const fetchUser = createThunk(fetchUserDataAsync, 'fetch-user');

const initialState = {
  data: null,
  loading: false,
  error: null,
};

function reducer(state = initialState, action) {
  switch (action.type) {
    case fetchUser.type.request:
      return {
        ...state,
        loading: true,
        error: null,
      };
    case fetchUser.type.success:
      return {
        ...state,
        data: action.payload,
        loading: false,
        error: null,
      };
    case fetchUser.type.error:
      return {
        ...state,
        loading: false,
        error: action.error,
      };
    default:
      return state;
  }
}

export const userProfileScope = createScope('user', reducer, { fetchUser });

Let's say fetchUserDataAsync looks like this:

function fetchUserDataAsync(userId, extraParam) {
  return UserApi.getUser(id, extraParam);
}

fetchUser thunk will dispatch 2 actions: request, and success or error, that will look like this:

dispatch(fetchUser('id-123', true));

const requestAction = {
  type: 'user/fetch-user/request',
  request: ['id-123', true],
};

const successAction = {
  type: 'user/fetch-user/success',
  request: ['id-123', true],
  payload: {
    /* result of api call */
  },
};

const errorAction = {
  type: 'user/fetch-user/error',
  request: ['id-123', true],
  error: {
    /* caught error */
  },
};

Composing Scopes

Redux scopes can be composed using combineScopes, analogous to how reducers can be composed using combineReducers.

We have already created two modules/scopes named user and preferences. Now, let's create a third module named favorites to illustrate how scope composition works.

src/modules/favorites/redux.js

import { createScope, createAction, createSelector } from 'redux-scope';

export const addToFavorites = createAction('add-to-favorites');

function reducer(state = [], action) {
  switch(action.type) {
    case addToFavorites.type:
      return [...state, action.payload],
    default:
      return state;
  }
}

export const getFavorites = createSelector(); // by default you select state => state
export const favoritesScope = createScope('favorites', reducer, {
  addToFavorites,
  getFavorites,
});

Say we want to combine together favorites and preferences to form a new module named user-stuff:

src/modules/user-stuff/redux.js

import { combineScopes } from 'redux-scope';
import { preferencesScope } from 'src/modules/preferences';
import { favoritesScope } from 'src/modules/favorites';

export userStuffScope = combineScopes('user-stuff', { preferencesScope, favoritesScope })

Now, at the top level:

src/app.js

import { createStore } from 'redux';
import thunk from 'redux-thunk';
import { createRootReducer } from 'redux-scope';
import { userScope } from 'src/modules/user';
import { userStuffScope } from 'src/modules/user-stuff';

const rootReducer = createRootReducer({
  userScope,
  userStuffScope,
});

const store = createStore(rootReducer, applyMiddleware(thunk));

Features

Shape of the resulting state

✨ Generated root reducer from the last example produces state with the following shape:

{
  "user": {
    "data": null,
    "error": null,
    "loading": false
  },
  "user-stuff": {
    "preferences": {
      "fontSize": "small"
    },
    "favorites": []
  }
}

Action types are scoped automatically

Composing scopes automatically prefixes action types with scope names of all the parent scopes. Say, if we dispatch following actions:

dispatch(addToFavorites({ userId: 'id-123' }));
dispatch(setFontSize('large'));
dispatch(fetchUser('id-123', true));

created actions would have automatically scoped action types:

'user-stuff/favorites/add-to-favorites'

'user-stuff/preferences/set-font-size'

'user/fetch-user/request'
'user/fetch-user/success'
'user/fetch-user/error'

Selectors stay wired correctly

✨ All selectors are wired automatically, they recieve root state and work everywhere:

loading(state); // false
fontSize(state); // 'small'

✨ No matter where you import and use your selectors, you always pass the root state, no need to pass the substate selector manually.

✨ The mechanism of nesting scopes using composeScopes makes sure all selectors remain connected to the right part of the state 🔬

✨ Your modules do not need to know where their reducer will be mounted, thus you get enhanced modularity.

✨ You can use your selectors like any other selector, compose them or use them with reselect.

Interop with plain Redux

Connecting external reducer to Redux scope

import { createScope } from 'redux-scope';
import { reducer } from 'src/modules/external-module';

export const externalScope = createScope('some-external-module', reducer);

Exporting reducer to use with plain Redux

Provide a path to the mounting point so that selectors can work correctly:

src/modules/module-that-uses-redux-scope/index.js

import { createRootReducer } from 'redux-scope';
import { userScope } from 'src/modules/user';
import { userStuffScope } from 'src/modules/user-stuff';

export const reducer = createRootReducer(
  {
    userScope,
    userStuffScope,
  },
  state => state.pathToThisModule,
);

Now you can use exported reducer like any other reducer, compose it with combineReducers, and all actions and selectors inside your module will work correctly.