Motivation

I have been struggling to find a state management solution for react that makes you interact with your state using plain functions as a baseline. Most of the alternatives I found compromise simplicity, they're verbose or super abstract. I wanted an option that didn't force me to adopt a specific data pattern and was lean.

I don't like boilerplate code. It's the main reason why I stopped using redux, but I never stopped chasing most of its design goals. I love how in redux, components can be built in isolation, tested easily, and its overall separation of concerns.

While using some of the available redux alternatives, I kept asking myself:

• "Where is the connect function?".
• "How do I attach the state to my component without rewriting it?".

This led to many awkward implementations attempts, that ultimately fell short one way or another.

I also love TypeScript, and it has been hard to find a well balanced solution that satisfied all my requirements as well as having strong type support.

Last but not least: your state management should be easy to understand for someone that didn't participate in the project design choices.

Design Goals

• [x] Be as simple as a mozzarella (duh!)
• [x] Use immutability without it getting in the way
• [x] Use plain JS functions as actions
• [x] Use async or sync functions for actions
• [x] Keep actions separated from the store
• [x] Prevent unnecessary re-rendering of components
• [x] Batch changes together to prevent race conditions
• [ ] Batch changes across multiple stores
• [x] Lean and robust TypeScript support
• [ ] Add dependencies checks (react-hooks/exhaustive-deps) for useDerivedState hook
• [ ] Implement concurrency controls similar to ember-concurrency

Install

$ yarn add --dev --exact mozzarella immer react-fast-compare

Basic Example (try it)

import React from 'react'
import ReactDOM from 'react-dom'
import { createStore } from 'mozzarella'

// create a store and pass an initial state

const { getState, createAction, useDerivedState } = createStore({
  names: ['kilian', 'arianna', 'antonia', 'pasquale'],
  places: ['san francisco', 'gavardo', 'salò']
})

// a Immer Draft<S> is passed to the action creator

const addName = createAction((state, name: string) => {
  state.names.push(name)
})

const addPlace = createAction((state, name: string) => {
  state.places.push(name)
})

// this component only re-renders when `state.names` changes

const Names = () => {
  console.info('<Names /> re-render')
  const names = useDerivedState(state => state.names)

  return (
    <div>
      <button onClick={() => addName('prison mike')}>Add Prison Mike</button>
      <button onClick={() => addPlace('scranton')}>Add Scranton</button>
      <h2>Names:</h2>
      <ul>
        {names.map((name, key) => (
          <li key={key}>{name}</li>
        ))}
      </ul>
      <h2>State:</h2>
      <pre>{JSON.stringify(getState(), null, 2)}</pre>
    </div>
  )
}

ReactDOM.render(<Names />, document.getElementById('root'))

Example with pure functional components (try it)

// store.ts

import { createStore } from 'mozzarella'

export const { getState, createAction, useDerivedState } = createStore({
  fruits: []
})

// actions.ts

import { createAction } from './store'

export const addFruit = createAction((state, name: string) => {
  state.fruits.push(name)
})

export const popFruit = createAction((state) => {
  state.fruits.pop()
})

// fruits.tsx

import React, { FC } from 'react'
import * as actions from './actions'
import { useDerivedState } from './store'

type FruitsProps = {
  fruits: string[]
  onRemove: () => void
  onAdd: (name: string) => void
}

// use this in your component stories and docs
export const Fruits = ({ fruits, onRemove, onAdd }: FruitsProps) => (
  <div>
    <h2>Fruits:</h2>
    <ul>
      {fruits.map((fruit, key) => (
        <li key={key}>{fruit}</li>
      ))}
    </ul>
    <button onClick={onRemove}>remove last fruit</button>
    <button onClick={() => onAdd('bananas')}>add bananas</button>
  </div>
)

// use this in your app rendering tree
Fruits.Connected = (() => {
  const derivedProps = useDerivedState((state) => ({
    fruits: state.fruits,
    onAdd: actions.addFruit,
    onRemove: actions.popFruit
  }))

  return <Fruits {...derivedProps} />
}) as FC

// index.tsx

import React from 'react'
import ReactDOM from 'react-dom'
import { Fruit } from './fruit'

export const App = () => (
  <Fruit.Connected />
)

ReactDOM.render(<App />, document.getElementById('app'))

API Reference

createStore

createStore <S>(initialState: S) => {
  getState: () => S
  useDerivedState: <R>(selector: (state: S) => R) => R
  createAction: <U extends unknown[]>(actionFn: (state: Draft<S>, ...params: U) => void) => (...params: U) => void
}

Takes the initial state as parameter and returns an object with three properties:

• getState
• createAction
• useDerivedState

Example

type State = {
  users: Record<User>,
  photos: Record<Photo>,
  albums: Record<Album>,
  likes?: Record<Likes>
}

const { getState, createAction, useDerivedState } = createStore<State>({
  users: {},
  photos: {},
  albums: {}
})

getState

const getState = () => S

Returns the instance of your immutable state

Example

const { likes } = getState()

createAction

const createAction = <U extends unknown[]>(actionFn: (state: Draft<S>, ...params: U) => void): (...params: U) => void

Takes a function as input and returns a closured action function that can manipulate a Draft<S> of your state.

Examples

API call

const login = createAction(async (state, email: string, password: string) => {
  const {
    err,
    userId,
    apiToken
  } = await apiRequest('/auth', { email, password })

  state.auth = {
    err,
    userId,
    apiToken
  }
})

// ...
<div>
  {auth.err ? <h1>Error: {err.message}</h1> : null}
  <button onClick={() => login('[email protected]', 'password')}>
    login
  </button>
</div>
// ...

Nested actions

const fetchUsers = createAction(async (state, amount: number) => {
  const data = await apiRequest('https://url/data')

  data.users.forEach((user) => {
    state.users[user.id] = user
  })

  setPhotos(data.photos)
})

// actions that don't use a draft state directly, can be regular functions
const setPhotos = (photos: Photo[]) => {
  photos.forEach(setPhoto)
}

// actions that mutate the state draft, use `createAction`
const setPhoto = createAction((state, photo: Photo) => {
  // all mutations in the same tick, use the same draft
  // they only trigger a re-render once per tick
  state.photos[photo.id] = photo
})

Batching state changes

const changeName = createAction((state, name: string) => {
  state.name = name
})

for (let i = 0; i < 100; i++) {
  // each iteration reuses the same state draft
  changeName(`name_${i}`)
}

// components subscribed to `state.name` will only re-render once.
// `state.name` will only be set once to "name_99"

useDerivedState

const useDerivedState: <R>(selector: (state: S) => R, dependencies?: DependencyList) => R

Hook that given a selector function, will return the output of the selector and re-render the component only when it changes.

As per usual, this hook takes an optional dependencies parameter that defaults to []`.

Example

const UserProfile = (props: { user: User, photos: Photo[] }) => {
  return (
    <div>
      <h1>User Profile: {props.user.username} ({props.photos.length} photos)</h1>
      <div>
        {props.photos.map((photo) => <Photo key={photo.id} photo={photo} />)}
      </div>
    </div>
  )
}

UserProfile.connected = (props: { userId: string }) => {
  const derivedProps = useDerivedState((state) => {
    user: state.users[props.userId],
    photos: Object.values(state.photos).filter((photo) => photo.userId === props.userId)
  }, [props.userId])

  return <UserProfile {...derivedProps} />
}

Or if you're not being dogmatic about it, or simply not implementing a strict design system:

const UserProfile = (props: { userId: string }) => {
  const { user, photos } = useDerivedState((state) => {
    user: state.users[props.userId],
    photos: Object.values(state.photos).filter((photo) => photo.userId === props.userId)
  }, [props.userId])

  return (
    <div>
      <h1>User Profile: {user.username} ({photos.length} photos)</h1>
      <div>
        {photos.map((photo) => <Photo key={photo.id} photo={photo} />)}
      </div>
    </div>
  )
}

How to contribute

Contributions and bug fixes from the community are welcome. You can run the test suite locally with:

$ yarn lint
$ yarn test

License

This software is released under the MIT license cited below.

Copyright (c) 2020 Kilian Ciuffolo, [email protected]. All Rights Reserved.

Permission is hereby granted, free of charge, to any person
obtaining a copy of this software and associated documentation
files (the 'Software'), to deal in the Software without
restriction, including without limitation the rights to use,
copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following
conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.