slices-pattern.md

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Slices Pattern	14

Slicing the store into smaller stores

Your store can become bigger and bigger and tougher to maintain as you add more features.

You can divide your main store into smaller individual stores to achieve modularity. This is simple to accomplish in Zustand!

The first individual store:

export const createFishSlice = (set) => ({
  fishes: 0,
  addFish: () => set((state) => ({ fishes: state.fishes + 1 })),
})

Another individual store:

export const createBearSlice = (set) => ({
  bears: 0,
  addBear: () => set((state) => ({ bears: state.bears + 1 })),
  eatFish: () => set((state) => ({ fishes: state.fishes - 1 })),
})

You can now combine both the stores into one bounded store:

import { create } from 'zustand'
import { createBearSlice } from './bearSlice'
import { createFishSlice } from './fishSlice'

export const useBoundStore = create((...a) => ({
  ...createBearSlice(...a),
  ...createFishSlice(...a),
}))

Usage in a React component

import { useBoundStore } from './stores/useBoundStore'

function App() {
  const bears = useBoundStore((state) => state.bears)
  const fishes = useBoundStore((state) => state.fishes)
  const addBear = useBoundStore((state) => state.addBear)
  return (
    <div>
      <h2>Number of bears: {bears}</h2>
      <h2>Number of fishes: {fishes}</h2>
      <button onClick={() => addBear()}>Add a bear</button>
    </div>
  )
}

export default App

Updating multiple stores

You can update multiple stores, at the same time, in a single function.

export const createBearFishSlice = (set, get) => ({
  addBearAndFish: () => {
    get().addBear()
    get().addFish()
  },
})

Combining all the stores together is the same as before.

import { create } from 'zustand'
import { createBearSlice } from './bearSlice'
import { createFishSlice } from './fishSlice'
import { createBearFishSlice } from './createBearFishSlice'

export const useBoundStore = create((...a) => ({
  ...createBearSlice(...a),
  ...createFishSlice(...a),
  ...createBearFishSlice(...a),
}))

Adding middlewares

Adding middlewares to a combined store is the same as with other normal stores.

Adding persist middleware to our useBoundStore:

import { create } from 'zustand'
import { createBearSlice } from './bearSlice'
import { createFishSlice } from './fishSlice'
import { persist } from 'zustand/middleware'

export const useBoundStore = create(
  persist(
    (...a) => ({
      ...createBearSlice(...a),
      ...createFishSlice(...a),
    }),
    { name: 'bound-store' },
  ),
)

Please keep in mind you should only apply middlewares in the combined store. Applying them inside individual slices can lead to unexpected issues.

Usage with TypeScript

A detailed guide on how to use the slice pattern in Zustand with TypeScript can be found here.