A small, fast and scaleable bearbones state-management solution. Has a comfy api based on hooks, isn't boilerplatey or opinionated, but still just enough to be explicit and flux-like.

Don't disregard it because it's cute. It has quite the claws, lots of time was spent to deal with common pitfalls, like the dreaded zombie child problem, react concurrency, and context loss between mixed renderers. It may be the one state-manager in the React space that gets all of these right.

You can try a live demo here.

npm install zustand

First create a store

Your store is a hook! You can put anything in it: primitives, objects, functions. The set function merges state.

import create from 'zustand'

const useStore = create(set => ({
  bears: 0,
  increasePopulation: () => set(state => ({ bears: state.bears + 1 })),
  removeAllBears: () => set({ bears: 0 })
}))

Then bind your components, and that's it!

Use the hook anywhere, no providers needed. Select your state and the component will re-render on changes.

function BearCounter() {
  const bears = useStore(state => state.bears)
  return <h1>{bears} around here ...</h1>
}

function Controls() {
  const increasePopulation = useStore(state => state.increasePopulation)
  return <button onClick={increasePopulation}>one up</button>
}

Why zustand over react-redux?

Simple and un-opinionated
Makes hooks the primary means of consuming state
Doesn't wrap your app in context providers
Can inform components transiently (without causing render)

Recipes

Fetching everything

You can, but bear in mind that it will cause the component to update on every state change!

const state = useStore()

Selecting multiple state slices

It detects changes with strict-equality (old === new) by default, this is efficient for atomic state picks.

const nuts = useStore(state => state.nuts)
const honey = useStore(state => state.honey)

If you want to construct a single object with multiple state-picks inside, similar to redux's mapStateToProps, you can tell zustand that you want the object to be diffed shallowly by passing an alternative equality function.

import shallow from 'zustand/shallow'

// Object pick, re-renders the component when either state.nuts or state.honey change
const { nuts, honey } = useStore(state => ({ nuts: state.nuts, honey: state.honey }), shallow)

// Array pick, re-renders the component when either state.nuts or state.honey change
const [nuts, honey] = useStore(state => [state.nuts, state.honey], shallow)

// Mapped picks, re-renders the component when state.treats changes in order, count or keys
const treats = useStore(state => Object.keys(state.treats), shallow)

Fetching from multiple stores

Since you can create as many stores as you like, forwarding results to succeeding selectors is as natural as it gets.

const currentBear = useCredentialsStore(state => state.currentBear)
const bear = useBearStore(state => state.bears[currentBear])

Memoizing selectors

It is generally recommended to memoize selectors with useCallback. This will prevent unnecessary computations each render. It also allows React to optimize performance in concurrent mode.

const fruit = useStore(useCallback(state => state.fruits[id], [id]))

If a selector doesn't depend on scope, you can define it outside the render function to obtain a fixed reference without useCallback.

const selector = state => state.berries

function Component() {
  const berries = useStore(selector)

Overwriting state

The set function has a second argument, false by default. Instead of merging, it will replace the state model. Be careful not to wipe out parts you rely on, like actions.

import omit from "lodash-es/omit"

const useStore = create(set => ({
  salmon: 1,
  tuna: 2,
  deleteEverything: () => set({ }, true), // clears the entire store, actions included
  deleteTuna: () => set(state => omit(state, ['tuna']), true)
}))

Async actions

Just call set when you're ready, zustand doesn't care if your actions are async or not.

const useStore = create(set => ({
  fishies: {},
  fetch: async pond => {
    const response = await fetch(pond)
    set({ fishies: await response.json() })
  }
}))

Read from state in actions

set allows fn-updates set(state => result), but you still have access to state outside of it through get.

const useStore = create((set, get) => ({
  sound: "grunt",
  action: () => {
    const sound = get().sound
    // ...
  }
})

Reading/writing state and reacting to changes outside of components

Sometimes you need to access state in a non-reactive way, or act upon the store. For these cases the resulting hook has utility functions attached to its prototype.

const useStore = create(() => ({ paw: true, snout: true, fur: true }))

// Getting non-reactive fresh state
const paw = useStore.getState().paw
// Listening to all changes, fires on every change
const unsub1 = useStore.subscribe(console.log)
// Listening to selected changes, in this case when "paw" changes
const unsub2 = useStore.subscribe(console.log, state => state.paw)
// Subscribe also supports an optional equality function
const unsub3 = useStore.subscribe(console.log, state => [state.paw, state.fur], shallow)
// Subscribe also exposes the previous value
const unsub4 = useStore.subscribe((paw, previousPaw) => console.log(paw, previousPaw), state => state.paw)
// Updating state, will trigger listeners
useStore.setState({ paw: false })
// Unsubscribe listeners
unsub1()
unsub2()
unsub3()
unsub4()
// Destroying the store (removing all listeners)
useStore.destroy()

// You can of course use the hook as you always would
function Component() {
  const paw = useStore(state => state.paw)

Using zustand without React

Zustands core can be imported and used without the React dependency. The only difference is that the create function does not return a hook, but the api utilities.

import create from 'zustand/vanilla'

const store = create(() => ({ ... }))
const { getState, setState, subscribe, destroy } = store

You can even consume an existing vanilla store with React:

import create from 'zustand'
import vanillaStore from './vanillaStore'

const useStore = create(vanillaStore)

Transient updates (for often occuring state-changes)

The subscribe function allows components to bind to a state-portion without forcing re-render on changes. Best combine it with useEffect for automatic unsubscribe on unmount. This can make a drastic performance impact when you are allowed to mutate the view directly.

const useStore = create(set => ({ scratches: 0, ... }))

function Component() {
  // Fetch initial state
  const scratchRef = useRef(useStore.getState().scratches)
  // Connect to the store on mount, disconnect on unmount, catch state-changes in a reference
  useEffect(() => useStore.subscribe(
    scratches => (scratchRef.current = scratches), 
    state => state.scratches
  ), [])

Sick of reducers and changing nested state? Use Immer!

Reducing nested structures is tiresome. Have you tried immer?

import produce from 'immer'

const useStore = create(set => ({
  lush: { forest: { contains: { a: "bear" } } },
  set: fn => set(produce(fn)),
}))

const set = useStore(state => state.set)
set(state => {
  state.lush.forest.contains = null
})

Middleware

You can functionally compose your store any way you like.

// Log every time state is changed
const log = config => (set, get, api) => config(args => {
  console.log("  applying", args)
  set(args)
  console.log("  new state", get())
}, get, api)

// Turn the set method into an immer proxy
const immer = config => (set, get, api) => config(fn => set(produce(fn)), get, api)

const useStore = create(
  log(
    immer((set) => ({
      bees: false,
      setBees: (input) => set((state) => void (state.bees = input)),
    })),
  ),
)

How to pipe middlewares

import create from "zustand"
import produce from "immer"
import pipe from "ramda/es/pipe"

/* log and immer functions from previous example */
/* you can pipe as many middlewares as you want */
const createStore = pipe(log, immer, create)

const useStore = createStore(set => ({
  bears: 1,
  increasePopulation: () => set(state => ({ bears: state.bears + 1 }))
}))

export default useStore

For a TS example see the following discussion

How to type immer middleware in TypeScript

import { State, StateCreator } from 'zustand'
import produce, { Draft } from 'immer'

const immer = <T extends State>(
  config: StateCreator<T, (fn: (draft: Draft<T>) => void) => void>
): StateCreator<T> => (set, get, api) =>
  config((fn) => set(produce(fn) as (state: T) => T), get, api)

Persist middleware

You can persist you store's data using any kind of storage.

import create from "zustand"
import { persist } from "zustand/middleware"

export const useStore = create(persist(
  (set, get) => ({
    fishes: 0,
    addAFish: () => set({ fish: get().fish + 1 })
  }),
  {
    name: "food-storage", // unique name
    getStorage: () => sessionStorage, // (optional) by default the 'localStorage' is used
  }
))

Can't live without redux-like reducers and action types?

const types = { increase: "INCREASE", decrease: "DECREASE" }

const reducer = (state, { type, by = 1 }) => {
  switch (type) {
    case types.increase: return { grumpiness: state.grumpiness + by }
    case types.decrease: return { grumpiness: state.grumpiness - by }
  }
}

const useStore = create(set => ({
  grumpiness: 0,
  dispatch: args => set(state => reducer(state, args)),
}))

const dispatch = useStore(state => state.dispatch)
dispatch({ type: types.increase, by: 2 })

Or, just use our redux-middleware. It wires up your main-reducer, sets initial state, and adds a dispatch function to the state itself and the vanilla api. Try this example.

import { redux } from 'zustand/middleware'

const useStore = create(redux(reducer, initialState))

Calling actions outside a React event handler

Because React handles setState synchronously if it's called outside an event handler. Updating the state outside an event handler will force react to update the components synchronously, therefore adding the risk of encountering the zombie-child effect. In order to fix this, the action needs to be wrapped in unstable_batchedUpdates

import { unstable_batchedUpdates } from 'react-dom' // or 'react-native'

const useStore = create((set) => ({
  fishes: 0,
  increaseFishes: () => set((prev) => ({ fishes: prev.fishes + 1 }))
}))

const nonReactCallback = () => {
  unstable_batchedUpdates(() => {
    useStore.getState().increaseFishes()
  })
}

More details: pmndrs#302

Redux devtools

import { devtools } from 'zustand/middleware'

// Usage with a plain action store, it will log actions as "setState"
const useStore = create(devtools(store))
// Usage with a redux store, it will log full action types
const useStore = create(devtools(redux(reducer, initialState)))

devtools takes the store function as its first argument, optionally you can name the store with a second argument: devtools(store, "MyStore"), which will be prefixed to your actions.

TypeScript

type State = {
  bears: number
  increase: (by: number) => void
}

const useStore = create<State>(set => ({
  bears: 0,
  increase: (by) => set(state => ({ bears: state.bears + by })),
}))

You can also use an interface:

import { State } from 'zustand';

interface BearState extends State {
  bears: number
  increase: (by: number) => void
}

Or, use combine and let tsc infer types.

import { combine } from 'zustand/middleware'

const useStore = create(
  combine(
    { bears: 0 }, 
    (set) => ({ increase: (by: number) => set((state) => ({ bears: state.bears + by })) })
  ),
)

Testing

For information regarding testing with Zustand, visit the dedicated Wiki page.

cloudhubke / zustand Goto Github PK

zustand's Introduction