Zustand

Bear necessities for state management in React

State management React

pmndrs/zustand zustand-demo.pmnd.rs/zustand

README

A small, fast and scalable bearbones state-management solution using simplified flux principles. Has a comfy api based on hooks, isn't boilerplatey or opinionated.

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.

```bash
npm install zustand # or yarn add zustand
```

:warning: This readme is written for JavaScript users. If you are a TypeScript user, don't miss TypeScript Usage.

First create a store

Your store is a hook! You can put anything in it: primitives, objects, functions. State has to be updated immutably and the set function merges state to help it.

```jsx
import create from 'zustand'
const useBearStore = 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.

```jsx
function BearCounter() {
const bears = useBearStore((state) => state.bears)
return <h1>{bears} around here ...</h1>
}
function Controls() {
const increasePopulation = useBearStore((state) => state.increasePopulation)
return <button onClick={increasePopulation}>one up</button>
}
```

Why zustand over 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)

Why zustand over context?

- Less boilerplate

- Renders components only on changes

- Centralized, action-based state management

Recipes

Fetching everything

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

```jsx
const state = useBearStore()
```

Selecting multiple state slices

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

```jsx
const nuts = useBearStore((state) => state.nuts)
const honey = useBearStore((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 the shallow equality function.

```jsx
import shallow from 'zustand/shallow'
// Object pick, re-renders the component when either state.nuts or state.honey change
const { nuts, honey } = useBearStore(
(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] = useBearStore(
(state) => [state.nuts, state.honey],
shallow
)
// Mapped picks, re-renders the component when state.treats changes in order, count or keys
const treats = useBearStore((state) => Object.keys(state.treats), shallow)
```

For more control over re-rendering, you may provide any custom equality function.

```jsx
const treats = useBearStore(
(state) => state.treats,
(oldTreats, newTreats) => compare(oldTreats, newTreats)
)
```

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.

```jsx
import omit from 'lodash-es/omit'
const useFishStore = 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.

```jsx
const useFishStore = 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.

```jsx
const useSoundStore = 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.

```jsx
const useDogStore = create(() => ({ paw: true, snout: true, fur: true }))
// Getting non-reactive fresh state
const paw = useDogStore.getState().paw
// Listening to all changes, fires synchronously on every change
const unsub1 = useDogStore.subscribe(console.log)
// Updating state, will trigger listeners
useDogStore.setState({ paw: false })
// Unsubscribe listeners
unsub1()
// Destroying the store (removing all listeners)
useDogStore.destroy()
// You can of course use the hook as you always would
const Component = () => {
const paw = useDogStore((state) => state.paw)
...
```

Using subscribe with selector

If you need to subscribe with selector,

subscribeWithSelector middleware will help.

With this middleware subscribe accepts an additional signature:

```ts
subscribe(selector, callback, options?: { equalityFn, fireImmediately }): Unsubscribe
```

```js
import { subscribeWithSelector } from 'zustand/middleware'
const useDogStore = create(
subscribeWithSelector(() => ({ paw: true, snout: true, fur: true }))
)
// Listening to selected changes, in this case when "paw" changes
const unsub2 = useDogStore.subscribe((state) => state.paw, console.log)
// Subscribe also exposes the previous value
const unsub3 = useDogStore.subscribe(
(state) => state.paw,
(paw, previousPaw) => console.log(paw, previousPaw)
)
// Subscribe also supports an optional equality function
const unsub4 = useDogStore.subscribe(
(state) => [state.paw, state.fur],
console.log,
{ equalityFn: shallow }
)
// Subscribe and fire immediately
const unsub5 = useDogStore.subscribe((state) => state.paw, console.log, {
fireImmediately: true,
})
```

Using zustand without React

Zustand 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.

```jsx
import create from 'zustand/vanilla'
const store = create(() => ({ ... }))
const { getState, setState, subscribe, destroy } = store
```

You can even consume an existing vanilla store with React:

```jsx
import create from 'zustand'
import vanillaStore from './vanillaStore'
const useBoundStore = create(vanillaStore)
```

:warning: Note that middlewares that modify set or get are not applied to getState and setState.

Transient updates (for often occurring 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.

```jsx
const useScratchStore = create(set => ({ scratches: 0, ... }))
const Component = () => {
// Fetch initial state
const scratchRef = useRef(useScratchStore.getState().scratches)
// Connect to the store on mount, disconnect on unmount, catch state-changes in a reference
useEffect(() => useScratchStore.subscribe(
state => (scratchRef.current = state.scratches)
), [])
...
```

Sick of reducers and changing nested state? Use Immer!

Reducing nested structures is tiresome. Have you tried immer?

```jsx
import produce from 'immer'
const useLushStore = create((set) => ({
lush: { forest: { contains: { a: 'bear' } } },
clearForest: () =>
set(
produce((state) => {
state.lush.forest.contains = null
})
),
}))
const clearForest = useLushStore((state) => state.clearForest)
clearForest()
```

Alternatively, there are some other solutions.

Middleware

You can functionally compose your store any way you like.

```jsx
// 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
)
const useBeeStore = create(
log((set) => ({
bees: false,
setBees: (input) => set({ bees: input }),
}))
)
```

Persist middleware

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

```jsx
import create from 'zustand'
import { persist } from 'zustand/middleware'
const useFishStore = create(
persist(
(set, get) => ({
fishes: 0,
addAFish: () => set({ fishes: get().fishes + 1 }),
}),
{
name: 'food-storage', // unique name
getStorage: () => sessionStorage, // (optional) by default, 'localStorage' is used
}
)
)
```

See the full documentation for this middleware.

Immer middleware

Immer is available as middleware too.

```jsx
import create from 'zustand'
import { immer } from 'zustand/middleware/immer'
const useBeeStore = create(
immer((set) => ({
bees: 0,
addBees: (by) =>
set((state) => {
state.bees += by
}),
}))
)
```

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

```jsx
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 useGrumpyStore = create((set) => ({
grumpiness: 0,
dispatch: (args) => set((state) => reducer(state, args)),
}))
const dispatch = useGrumpyStore((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.

```jsx
import { redux } from 'zustand/middleware'
const useGrumpyStore = create(redux(reducer, initialState))
```

Redux devtools

```jsx
import { devtools } from 'zustand/middleware'
// Usage with a plain action store, it will log actions as "setState"
const usePlainStore = create(devtools(store))
// Usage with a redux store, it will log full action types
const useReduxStore = create(devtools(redux(reducer, initialState)))
```

devtools takes the store function as its first argument, optionally you can name the store or configure serialize options with a second argument.

Name store: devtools(store, {name: "MyStore"}), which will create a separate instance named "MyStore" in the devtools.

Serialize options: devtools(store, { serialize: { options: true } }).

Logging Actions

devtools will only log actions from each separated store unlike in a typical _combined reducers_ redux store. See an approach to combining stores https://github.com/pmndrs/zustand/issues/163

You can log a specific action type for each set function by passing a third parameter:

```jsx
const createBearSlice = (set, get) => ({
eatFish: () =>
set(
(prev) => ({ fishes: prev.fishes > 1 ? prev.fishes - 1 : 0 }),
false,
'bear/eatFish'
),
})
```

You can also log action's type along with its payload:

```jsx
const createBearSlice = (set, get) => ({
addFishes: (count) =>
set((prev) => ({ fishes: prev.fishes + count }), false, {
type: 'bear/addFishes',
count,
}),
})
```

If an action type is not provided, it is defaulted to "anonymous". You can customize this default value by providing an anonymousActionType parameter:

```jsx
devtools(..., { anonymousActionType: 'unknown', ... })
```

If you wish to disable devtools (on production for instance). You can customize this setting by providing the enabled parameter:

```jsx
devtools(..., { enabled: false, ... })
```

React context

The store created with create doesn't require context providers. In some cases, you may want to use contexts for dependency injection or if you want to initialize your store with props from a component. Because the normal store is a hook, passing it as a normal context value may violate rules of hooks.

The recommended method available since v4 is to use vanilla store.

```jsx
import { createContext, useContext } from 'react'
import { createStore, useStore } from 'zustand'
const store = createStore(...) // vanilla store without hooks
const StoreContext = createContext()
const App = () => (
<StoreContext.Provider value={store}>
...
</StoreContext.Provider>
)
const Component = () => {
const store = useContext(StoreContext)
const slice = useStore(store, selector)
...
```

Alternatively, a special createContext is provided.

TypeScript Usage

Basic typescript usage doesn't require anything special except for writing `create()(...)` instead of `create(...)`...

```ts
import create from 'zustand'
import { devtools, persist } from 'zustand/middleware'
interface BearState {
bears: number
increase: (by: number) => void
}
const useBearStore = create<BearState>()(
devtools(
persist(
(set) => ({
bears: 0,
increase: (by) => set((state) => ({ bears: state.bears + by })),
}),
{
name: 'bear-storage',
}
)
)
)
```

A more complete TypeScript guide is here.

Best practices

- You may wonder how to organize your code for better maintenance: Splitting the store into separate slices.

- Recommended usage for this unopinionated library: Flux inspired practice.

- Calling actions outside a React event handler in pre React 18.

- Testing

3rd-Party Libraries

Some users may want to extends Zustand's feature set which can be done using 3rd-party libraries made by the community. For information regarding 3rd-party libraries with Zustand, visit the doc.

Comparison with other libraries

- Difference between zustand and valtio