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The Immer middleware enables you to use immutable state in a more convenient way. With Immer, you can simplify handling immutable data structures in Zustand by writing mutable-looking code that safely updates state.

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Installation

In order to use the Immer middleware in Zustand, you will need to install Immer as a direct dependency. 
npm install immer

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Usage

Notice the extra parentheses after the type parameter as mentioned in the TypeScript Guide.

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Updating Simple States

For simple state updates, Immer allows you to directly mutate the state object: 
import { create } from 'zustand'
import { immer } from 'zustand/middleware/immer'

type State = {
  count: number
}

type Actions = {
  increment: (qty: number) => void
  decrement: (qty: number) => void
}

export const useCountStore = create<State & Actions>()()
  immer((set) => ({
    count: 0,
    increment: (qty: number) =>
      set((state) => {
        state.count += qty
      }),
    decrement: (qty: number) =>
      set((state) => {
        state.count -= qty
      }),
  })),
)

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Updating Complex States

Immer really shines when working with deeply nested or complex state structures: 
import { create } from 'zustand'
import { immer } from 'zustand/middleware/immer'

interface Todo {
  id: string
  title: string
  done: boolean
}

type State = {
  todos: Record<string, Todo>
}

type Actions = {
  toggleTodo: (todoId: string) => void
}

export const useTodoStore = create<State & Actions>()()
  immer((set) => ({
    todos: {
      '82471c5f-4207-4b1d-abcb-b98547e01a3e': {
        id: '82471c5f-4207-4b1d-abcb-b98547e01a3e',
        title: 'Learn Zustand',
        done: false,
      },
      '354ee16c-bfdd-44d3-afa9-e93679bda367': {
        id: '354ee16c-bfdd-44d3-afa9-e93679bda367',
        title: 'Learn Jotai',
        done: false,
      },
      '771c85c5-46ea-4a11-8fed-36cc2c7be344': {
        id: '771c85c5-46ea-4a11-8fed-36cc2c7be344',
        title: 'Learn Valtio',
        done: false,
      },
      '363a4bac-083f-47f7-a0a2-aeeee153a99c': {
        id: '363a4bac-083f-47f7-a0a2-aeeee153a99c',
        title: 'Learn Signals',
        done: false,
      },
    },
    toggleTodo: (todoId: string) =>
      set((state) => {
        state.todos[todoId].done = !state.todos[todoId].done
      }),
  })),
)

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Gotchas

In this section you will find some things that you need to keep in mind when using Zustand with Immer.

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My subscriptions aren’t being called

If you are using Immer, make sure you are actually following the rules of Immer.
For class objects to work properly with Immer, you must add [immerable] = true to the class.
If you don’t do this, Immer will still mutate the object, but not as a proxy, so it will also update the current state. Zustand checks if the state has actually changed, so since both the current state and the next state are equal (if you don’t do it correctly), Zustand will skip calling the subscriptions.

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Live Demos

Basic Example

Simple counter example using Immer middleware

Advanced Example

Complex todo list with nested state updates

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