zustand

What is zustand?

Zustand is a state management library for React and other JavaScript applications. It provides a simple and flexible way to create and manage global state without the complexity of traditional solutions like Redux. Zustand uses a hook-based API to allow components to subscribe to state changes and define actions for updating the state.

What are zustand's main functionalities?

Creating a store

This code sample demonstrates how to create a store with Zustand. The store has a state with a 'fishes' property and an 'addFish' action to increment the number of fishes.

import create from 'zustand';

const useStore = create(set => ({
  fishes: 0,
  addFish: () => set(state => ({ fishes: state.fishes + 1 }))
}));

Subscribing to state changes

This code sample shows how a React component can subscribe to state changes. The 'FishCounter' component uses the 'useStore' hook to access the number of fishes from the store's state.

import React from 'react';
import useStore from './store';

function FishCounter() {
  const fishes = useStore(state => state.fishes);
  return <div>{fishes} fishes</div>;
}

Updating the state

This code sample illustrates how to update the state using an action defined in the store. The 'AddFishButton' component gets the 'addFish' action from the store and uses it as an onClick event handler.

import React from 'react';
import useStore from './store';

function AddFishButton() {
  const addFish = useStore(state => state.addFish);
  return <button onClick={addFish}>Add a fish</button>;
}

Other packages similar to zustand

redux

Redux is a predictable state container for JavaScript apps. It is more complex than Zustand, involving actions, reducers, and middleware, making it suitable for larger applications with more complex state management needs.

mobx

MobX is a state management library that uses observable state objects and reactions to automatically track changes and update the UI. It is more opinionated than Zustand and uses a different paradigm based on observables.

recoil

Recoil is a state management library for React that provides a more granular approach to managing state with atoms and selectors. It is similar to Zustand in its simplicity but offers more advanced features for derived state and asynchronous queries.

context

React Context API is not a package but a built-in feature of React for managing state. It is simpler than Zustand but can lead to performance issues in larger applications due to unnecessary re-renders.

README

npm install zustand

React state is in a bit of a mess. Hundreds of solutions out there, the established options don't exactly go along well with hooks, context does not scale enough. There are dozens of solutions that claim you can replace, say, Redux with hooks and context, but most can't select state, which IMO doesn't qualify as a state-manager. The ones that do scale and offer hooks with good ergonomics often come with other problems, like being unable to breach reconcilers (react-three-fiber, react-konva, etc).

zustand is a small barebones store. Nothing much to it, but it has a comfy api and solves some of these problems.

Create a store (or multiple, up to you...)

import create from 'zustand'

// Name your store anything you like, but remember, it's a hook!
const [useStore] = create(set => ({
  // Everything in here is your state
  count: 1,
  // You don't have to nest your actions, but makes it easier to fetch them later on
  actions: {
    inc: () => set(state => ({ count: state.count + 1 })), // same semantics as setState
    dec: () => set(state => ({ count: state.count - 1 })),
  },
}))

Bind components

function Counter() {
  // Will only re-render the component when "count" changes
  const count = useStore(state => state.count)
  return <h1>{count}</h1>
}

function Controls() {
  // "actions" isn't special, we just named it like that to fetch updaters easier 
  const { inc, dec } = useStore(state => state.actions)
  return (
    <>
      <button onClick={inc}>up</button>
      <button onClick={dec}>down</button>
    </>
  )
}

Receipes

Fetching everything

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

const data = useStore()

Selecting multiple state slices

It's just like mapStateToProps in Redux. zustand will run a small shallow equal over the object you return. Of course, it won't cause re-renders if these properties aren't changed in the state model.

const { name, age } = useStore(state => ({ name: state.name, age: state.age }))

Or, if you prefer, atomic selects do the same ...

const name = useStore(state => state.name)
const age = useStore(state => state.age)

Fetching from multiple stores

Since you can create as many stores as you like, forwarding a result into another selector is straight forward.

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

Memoizing selectors (this is completely optional)

You can change the selector always! But since you essentially pass a new function every render it will subscribe and unsubscribe to the store every time. It's not that much of a big deal, unless you're dealing with hundreds of connected components. But you can still memoize your selector with an optional second argument that's similar to Reacts useCallback. Give it the dependencies you are interested in and it will let your selector in peace.

const book = useBookStore(state => state.books[title], [title])

Async actions

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

const [useStore] = create(set => ({
  result: '',
  fetch: async url => {
    const response = await fetch(url)
    const json = await response.json()
    set({ result: json })
  },
}))

Read from state in actions

The set function already allows functional update set(state => result) but should there be cases where you need to access outside of it you have an optional get, too.

const [useStore] = create((set, get) => ({
  text: "hello",
  action: () => {
    const text = get().text
    ...
  }
})

Sick of reducers and changing nested state? Use Immer!

import produce from "immer"

const [useStore] = create(set => ({
  nested: {
    structure: {
      constains: {
        a: "value"
      }
    }
  },
  action: () => set(produce(draft => {
    draft.nested.structure.contains.a.value = undefined // not anymore ...
  }))
})

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(...)

// Listening to changes
api.subscribe(state => console.log("i log whenever state changes", state))
// Getting fresh state
const state = api.getState()
// Destroying the store
api.destroy()