npm install zustand

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

How to use it

First create a store (or multiple, up to you...)

Your store is a hook! There are no rules, you can put anything in it, atomics, objects, functions. Like Reacts setState, set merges state, and it has the exact same semantics.

import create from 'zustand'

const [useStore] = create(set => ({
  count: 0,
  increase: () => set(state => ({ count: state.count + 1 })),
  reset: () => set({ count: 0 })
}))

Then bind components with the resulting hook, that's it!

Use the hook anywhere, no providers needed. Once you have selected state your component will re-render on changes.

function Counter() {
  const count = useStore(state => state.count)
  return <h1>{count}</h1>
}

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

Why zustand over react-redux? This lib ...

1. is simpler and un-opinionated
2. makes hooks the primary means of consuming state
3. isn't strictly dependent on actions, types & dispatch
4. doesn't wrap your app into context providers (which allows it to support mixed reconcilers)
5. can access state outside of components (and even React)
6. has a solution for rapid state changes (look below for transient updates)
7. is (or can be made) compatible with the redux api

Recipes

Fetching everything

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

const state = useStore()

Selecting multiple state slices

zustand defaults to strict-equality (old === new) to detect changes, this is efficient for atomic state picks.

const foo = useStore(state => state.foo)
const bar = useStore(state => state.bar)

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.

import { shallowEqual } from 'zustand'

const { foo, bar } = useStore(state => ({ foo: state.foo, bar: state.bar }), shallowEqual)

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 currentUser = useCredentialsStore(state => state.currentUser)
const person = usePersonStore(state => state.persons[currentUser])

Memoizing selectors

Selectors run on state changes, as well as when the component renders. If you give zustand a fixed reference, it will only run on state changes, or when the selector changes. Don't worry about this, unless your selector is expensive.

const fooSelector = useCallback(state => state.foo[props.id], [props.id])
const foo = useStore(fooSelector)

Async actions

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

const [useStore] = create(set => ({
  json: {},
  fetch: async url => {
    const response = await fetch(url)
    set({ json: 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) => ({
  text: "hello",
  action: () => {
    const text = get().text

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 => ({
  nested: { structure: { contains: { a: "value" } } },
  set: fn => set(produce(fn)),
}))

const set = useStore(state => state.set)
set(state => void state.nested.structure.contains = null)

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 { count: state.count + by }
    case types.decrease: return { count: state.count - by }
  }
}

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

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

Reading/writing state and reacting to changes outside of components

You can use it with or without React out of the box.

const [, api] = create({ a: 1, b: 2, c: 3 })

// Getting fresh state
const num = api.getState().n
// Listening to all changes, fires on every dispatch
const unsub1 = api.subscribe(state => console.log("state changed", state))
// Listening to selected changes
const unsub2 = api.subscribe(state => state.a, a => console.log("a changed", a))
// Updating state, will trigger listeners
api.setState({ a: 1 })
// Unsubscribe listeners
unsub1()
unsub2()
// Destroying the store (removing all listeners)
api.destroy()

Transient updates (for often occuring state-changes)

The api signature of subscribe([selector,] callback):unsub allows you to easily bind a component to a store without forcing it to re-render on state changes, you will be notified in a callback instead. Best combine it with useEffect. This can make a drastic performance difference when you are allowed to mutate the view directly.

const [useStore, api] = create(set => ({ [0]: [-10, 0], [1]: [10, 5], ... }))

function Component({ id }) {
  // Fetch initial state
  const xy = useRef(api.getState()[id])
  // Connect to the store on mount, disconnect on unmount, catch state-changes in a callback
  useEffect(() => api.subscribe(state => state[id], coords => (xy.current = coords)), [id])

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 => ({
  text: "hello",
  setText: input => set(state => {
    state.text = input
  })
}))))

Devtools

Yes, it's currently being hashed out but you can already start using it: https://codesandbox.io/s/amazing-kepler-swxol. It works with regular actions as well, you don't need reducers for this.