Usage With TypeScript

What You'll Learn

Details on how to use each Redux Toolkit API with TypeScript

Introduction

Redux Toolkit is written in TypeScript, and its API is designed to enable great integration with TypeScript applications.

This page provides specific details for each of the different APIs included in Redux Toolkit and how to type them correctly with TypeScript.

See the TypeScript Quick Start tutorial page for a brief overview of how to set up and use Redux Toolkit and React Redux to work with TypeScript.

info

If you encounter any problems with the types that are not described on this page, please open an issue for discussion.

`configureStore`

The basics of using configureStore are shown in TypeScript Quick Start tutorial page. Here are some additional details that you might find useful.

Getting the `State` type

The easiest way of getting the State type is to define the root reducer in advance and extract its ReturnType.
It is recommended to give the type a different name like RootState to prevent confusion, as the type name State is usually overused.

import { combineReducers } from '@reduxjs/toolkit'
const rootReducer = combineReducers({})
export type RootState = ReturnType<typeof rootReducer>

Alternatively, if you choose to not create a rootReducer yourself and instead pass the slice reducers directly to configureStore(), you need to slightly modify the typing to correctly infer the root reducer:

import { configureStore } from '@reduxjs/toolkit'
// ...
const store = configureStore({
  reducer: {
    one: oneSlice.reducer,
    two: twoSlice.reducer,
  },
})
export type RootState = ReturnType<typeof store.getState>

export default store

If you pass the reducers directly to configureStore() and do not define the root reducer explicitly, there is no reference to rootReducer. Instead, you can refer to store.getState, in order to get the State type.

import { configureStore } from '@reduxjs/toolkit'
import rootReducer from './rootReducer'
const store = configureStore({
  reducer: rootReducer,
})
export type RootState = ReturnType<typeof store.getState>

Getting the `Dispatch` type

If you want to get the Dispatch type from your store, you can extract it after creating the store. It is recommended to give the type a different name like AppDispatch to prevent confusion, as the type name Dispatch is usually overused. You may also find it to be more convenient to export a hook like useAppDispatch shown below, then using it wherever you'd call useDispatch.

import { configureStore } from '@reduxjs/toolkit'
import { useDispatch } from 'react-redux'
import rootReducer from './rootReducer'

const store = configureStore({
  reducer: rootReducer,
})

export type AppDispatch = typeof store.dispatch
export const useAppDispatch: () => AppDispatch = useDispatch // Export a hook that can be reused to resolve types

export default store

Correct typings for the `Dispatch` type

The type of the dispatch function type will be directly inferred from the middleware option. So if you add correctly typed middlewares, dispatch should already be correctly typed.

As TypeScript often widens array types when combining arrays using the spread operator, we suggest using the .concat(...) and .prepend(...) methods of the Tuple returned by getDefaultMiddleware().

import { configureStore } from '@reduxjs/toolkit'
import additionalMiddleware from 'additional-middleware'
import logger from 'redux-logger'
// @ts-ignore
import untypedMiddleware from 'untyped-middleware'
import rootReducer from './rootReducer'

export type RootState = ReturnType<typeof rootReducer>
const store = configureStore({
  reducer: rootReducer,
  middleware: (getDefaultMiddleware) =>
    getDefaultMiddleware()
      .prepend(
        // correctly typed middlewares can just be used
        additionalMiddleware,
        // you can also type middlewares manually
        untypedMiddleware as Middleware<
          (action: Action<'specialAction'>) => number,
          RootState
        >
      )
      // prepend and concat calls can be chained
      .concat(logger),
})

export type AppDispatch = typeof store.dispatch

export default store

Using `Tuple` without `getDefaultMiddleware`

If you want to skip the usage of getDefaultMiddleware altogether, you are required to use Tuple for type-safe creation of your middleware array. This class extends the default JavaScript Array type, only with modified typings for .concat(...) and the additional .prepend(...) method.

For example:

import { configureStore, Tuple } from '@reduxjs/toolkit'

configureStore({
  reducer: rootReducer,
  middleware: () => new Tuple(additionalMiddleware, logger),
})

Using the extracted `Dispatch` type with React Redux

By default, the React Redux useDispatch hook does not contain any types that take middlewares into account. If you need a more specific type for the dispatch function when dispatching, you may specify the type of the returned dispatch function, or create a custom-typed version of useSelector. See the React Redux documentation for details.

`createAction`

For most use cases, there is no need to have a literal definition of action.type, so the following can be used:

createAction<number>('test')

This will result in the created action being of type PayloadActionCreator<number, string>.

In some setups, you will need a literal type for action.type, though. Unfortunately, TypeScript type definitions do not allow for a mix of manually-defined and inferred type parameters, so you'll have to specify the type both in the Generic definition as well as in the actual JavaScript code:

createAction<number, 'test'>('test')

If you are looking for an alternate way of writing this without the duplication, you can use a prepare callback so that both type parameters can be inferred from arguments, removing the need to specify the action type.

function withPayloadType<T>() {
  return (t: T) => ({ payload: t })
}
createAction('test', withPayloadType<string>())

Alternative to using a literally-typed `action.type`

If you are using action.type as a discriminator on a discriminated union, for example to correctly type your payload in case statements, you might be interested in this alternative:

Created action creators have a match method that acts as a type predicate:

const increment = createAction<number>('increment')
function test(action: Action) {
  if (increment.match(action)) {
    // action.payload inferred correctly here
    action.payload
  }
}

This match method is also very useful in combination with redux-observable and RxJS's filter method.

`createReducer`

Building Type-Safe Reducer Argument Objects

The second parameter for createReducer is a callback that receives a ActionReducerMapBuilder instance:

const increment = createAction<number, 'increment'>('increment')
const decrement = createAction<number, 'decrement'>('decrement')
createReducer(0, (builder) =>
  builder
    .addCase(increment, (state, action) => {
      // action is inferred correctly here
    })
    .addCase(decrement, (state, action: PayloadAction<string>) => {
      // this would error out
    })
)

Typing `builder.addMatcher`

As the first matcher argument to builder.addMatcher, a type predicate function should be used. As a result, the action argument for the second reducer argument can be inferred by TypeScript:

function isNumberValueAction(action: UnknownAction): action is PayloadAction<{ value: number }> {
  return typeof action.payload.value === 'number'
}

createReducer({ value: 0 }, builder =>
   builder.addMatcher(isNumberValueAction, (state, action) => {
      state.value += action.payload.value
   })
})

`createSlice`

As createSlice creates your actions as well as your reducer for you, you don't have to worry about type safety here. Action types can just be provided inline:

const slice = createSlice({
  name: 'test',
  initialState: 0,
  reducers: {
    increment: (state, action: PayloadAction<number>) => state + action.payload,
  },
})
// now available:
slice.actions.increment(2)
// also available:
slice.caseReducers.increment(0, { type: 'increment', payload: 5 })

If you have too many case reducers and defining them inline would be messy, or you want to reuse case reducers across slices, you can also define them outside the createSlice call and type them as CaseReducer:

type State = number
const increment: CaseReducer<State, PayloadAction<number>> = (state, action) =>
  state + action.payload

createSlice({
  name: 'test',
  initialState: 0,
  reducers: {
    increment,
  },
})

Defining the Initial State Type

You might have noticed that it is not a good idea to pass your SliceState type as a generic to createSlice. This is due to the fact that in almost all cases, follow-up generic parameters to createSlice need to be inferred, and TypeScript cannot mix explicit declaration and inference of generic types within the same "generic block".

The standard approach is to declare an interface or type for your state, create an initial state value that uses that type, and pass the initial state value to createSlice. You can also use the construct initialState: myInitialState as SliceState.

type SliceState = { state: 'loading' } | { state: 'finished'; data: string }

// First approach: define the initial state using that type
const initialState: SliceState = { state: 'loading' }

createSlice({
  name: 'test1',
  initialState, // type SliceState is inferred for the state of the slice
  reducers: {},
})

// Or, cast the initial state as necessary
createSlice({
  name: 'test2',
  initialState: { state: 'loading' } as SliceState,
  reducers: {},
})

which will result in a Slice<SliceState, ...>.

Defining Action Contents with `prepare` Callbacks

If you want to add a meta or error property to your action, or customize the payload of your action, you have to use the prepare notation.

Using this notation with TypeScript looks like this:

const blogSlice = createSlice({
  name: 'blogData',
  initialState,
  reducers: {
    receivedAll: {
      reducer(
        state,
        action: PayloadAction<Page[], string, { currentPage: number }>
      ) {
        state.all = action.payload
        state.meta = action.meta
      },
      prepare(payload: Page[], currentPage: number) {
        return { payload, meta: { currentPage } }
      },
    },
  },
})

Generated Action Types for Slices

createSlice generates action type strings by combining the name field from the slice with the field name of the reducer function, like 'test/increment'. This is strongly typed as the exact value, thanks to TS's string literal analysis.

You can also use the slice.action.myAction.match type predicate, which will narrow down an action object to the exact type:

const slice = createSlice({
  name: 'test',
  initialState: 0,
  reducers: {
    increment: (state, action: PayloadAction<number>) => state + action.payload,
  },
})

type incrementType = typeof slice.actions.increment.type
// type incrementType = 'test/increment'

function myCustomMiddleware(action: Action) {
  if (slice.actions.increment.match(action)) {
    // `action` is narrowed down to the type `PayloadAction<number>` here.
  }
}

If you actually need that type, unfortunately there is no other way than manual casting.

Type safety with `extraReducers`

Reducer lookup tables that map an action type string to a reducer function are not easy to fully type correctly. This affects both createReducer and the extraReducers argument for createSlice. So, like with createReducer, you should use the "builder callback" approach for defining the reducer object argument.

This is particularly useful when a slice reducer needs to handle action types generated by other slices, or generated by specific calls to createAction (such as the actions generated by createAsyncThunk).

const fetchUserById = createAsyncThunk(
  'users/fetchById',
  // if you type your function argument here
  async (userId: number) => {
    const response = await fetch(`https://reqres.in/api/users/${userId}`)
    return (await response.json()) as Returned
  }
)

interface UsersState {
  entities: []
  loading: 'idle' | 'pending' | 'succeeded' | 'failed'
}

const initialState = {
  entities: [],
  loading: 'idle',
} as UsersState

const usersSlice = createSlice({
  name: 'users',
  initialState,
  reducers: {
    // fill in primary logic here
  },
  extraReducers: (builder) => {
    builder.addCase(fetchUserById.pending, (state, action) => {
      // both `state` and `action` are now correctly typed
      // based on the slice state and the `pending` action creator
    })
  },
})

Like the builder in createReducer, this builder also accepts addMatcher (see typing builder.matcher) and addDefaultCase.

Payload with All Optional Fields

If you try to supply a payload type where all fields are optional, like PayloadAction<Partial<User>> or PayloadAction<{value?: string}>, TS may not be able to infer the action type correctly.

You can work around this by using a custom AtLeastOne utility type to help ensure that at least one of the fields must be passed in:

type AtLeastOne<T extends Record<string, any>> = keyof T extends infer K
  ? K extends string
    ? Pick<T, K & keyof T> & Partial<T>
    : never
  : never

// Use this type instead of `Partial<MyPayloadType>`
type AtLeastOneUserField = AtLeastOne<User>

Typing Async Thunks Inside `createSlice`

As of 2.0, createSlice allows defining thunks inside of reducers using a callback syntax.

Typing for the create.asyncThunk method works in the same way as createAsyncThunk, with one key difference.

A type for state and/or dispatch cannot be provided as part of the ThunkApiConfig, as this would cause circular types.

Instead, it is necessary to assert the type when needed - getState() as RootState. You may also include an explicit return type for the payload function as well, in order to break the circular type inference cycle.

create.asyncThunk<Todo, string, { rejectValue: { error: string } }>(
  // may need to include an explicit return type
  async (id: string, thunkApi): Promise<Todo> => {
    // Cast types for `getState` and `dispatch` manually
    const state = thunkApi.getState() as RootState
    const dispatch = thunkApi.dispatch as AppDispatch
    try {
      const todo = await fetchTodo()
      return todo
    } catch (e) {
      throw thunkApi.rejectWithValue({
        error: 'Oh no!',
      })
    }
  }
)

For common thunk API configuration options, a withTypes helper is provided:

reducers: (create) => {
  const createAThunk =
    create.asyncThunk.withTypes<{ rejectValue: { error: string } }>()

  return {
    fetchTodo: createAThunk<Todo, string>(async (id, thunkApi) => {
      throw thunkApi.rejectWithValue({
        error: 'Oh no!',
      })
    }),
    fetchTodos: createAThunk<Todo[], string>(async (id, thunkApi) => {
      throw thunkApi.rejectWithValue({
        error: 'Oh no, not again!',
      })
    }),
  }
}

Wrapping `createSlice`

If you need to reuse reducer logic, it is common to write "higher-order reducers" that wrap a reducer function with additional common behavior. This can be done with createSlice as well, but due to the complexity of the types for createSlice, you have to use the SliceCaseReducers and ValidateSliceCaseReducers types in a very specific way.

Here is an example of such a "generic" wrapped createSlice call:

interface GenericState<T> {
  data?: T
  status: 'loading' | 'finished' | 'error'
}

const createGenericSlice = <
  T,
  Reducers extends SliceCaseReducers<GenericState<T>>
>({
  name = '',
  initialState,
  reducers,
}: {
  name: string
  initialState: GenericState<T>
  reducers: ValidateSliceCaseReducers<GenericState<T>, Reducers>
}) => {
  return createSlice({
    name,
    initialState,
    reducers: {
      start(state) {
        state.status = 'loading'
      },
      /**
       * If you want to write to values of the state that depend on the generic
       * (in this case: `state.data`, which is T), you might need to specify the
       * State type manually here, as it defaults to `Draft<GenericState<T>>`,
       * which can sometimes be problematic with yet-unresolved generics.
       * This is a general problem when working with immer's Draft type and generics.
       */
      success(state: GenericState<T>, action: PayloadAction<T>) {
        state.data = action.payload
        state.status = 'finished'
      },
      ...reducers,
    },
  })
}

const wrappedSlice = createGenericSlice({
  name: 'test',
  initialState: { status: 'loading' } as GenericState<string>,
  reducers: {
    magic(state) {
      state.status = 'finished'
      state.data = 'hocus pocus'
    },
  },
})

`createAsyncThunk`

Basic `createAsyncThunk` Types

In the most common use cases, you should not need to explicitly declare any types for the createAsyncThunk call itself.

Just provide a type for the first argument to the payloadCreator argument as you would for any function argument, and the resulting thunk will accept the same type as its input parameter. The return type of the payloadCreator will also be reflected in all generated action types.

interface MyData {
  // ...
}

const fetchUserById = createAsyncThunk(
  'users/fetchById',
  // Declare the type your function argument here:
  async (userId: number) => {
    const response = await fetch(`https://reqres.in/api/users/${userId}`)
    // Inferred return type: Promise<MyData>
    return (await response.json()) as MyData
  }
)

// the parameter of `fetchUserById` is automatically inferred to `number` here
// and dispatching the resulting thunkAction will return a Promise of a correctly
// typed "fulfilled" or "rejected" action.
const lastReturnedAction = await store.dispatch(fetchUserById(3))

Typing the `thunkApi` Object

The second argument to the payloadCreator, known as thunkApi, is an object containing references to the dispatch, getState, and extra arguments from the thunk middleware as well as a utility function called rejectWithValue. If you want to use these from within the payloadCreator, you will need to define some generic arguments, as the types for these arguments cannot be inferred. Also, as TS cannot mix explicit and inferred generic parameters, from this point on you'll have to define the Returned and ThunkArg generic parameter as well.

Manually Defining `thunkApi` Types

To define the types for these arguments, pass an object as the third generic argument, with type declarations for some or all of these fields:

type AsyncThunkConfig = {
  /** return type for `thunkApi.getState` */
  state?: unknown
  /** type for `thunkApi.dispatch` */
  dispatch?: Dispatch
  /** type of the `extra` argument for the thunk middleware, which will be passed in as `thunkApi.extra` */
  extra?: unknown
  /** type to be passed into `rejectWithValue`'s first argument that will end up on `rejectedAction.payload` */
  rejectValue?: unknown
  /** return type of the `serializeError` option callback */
  serializedErrorType?: unknown
  /** type to be returned from the `getPendingMeta` option callback & merged into `pendingAction.meta` */
  pendingMeta?: unknown
  /** type to be passed into the second argument of `fulfillWithValue` to finally be merged into `fulfilledAction.meta` */
  fulfilledMeta?: unknown
  /** type to be passed into the second argument of `rejectWithValue` to finally be merged into `rejectedAction.meta` */
  rejectedMeta?: unknown
}

const fetchUserById = createAsyncThunk<
  // Return type of the payload creator
  MyData,
  // First argument to the payload creator
  number,
  {
    // Optional fields for defining thunkApi field types
    dispatch: AppDispatch
    state: State
    extra: {
      jwt: string
    }
  }
>('users/fetchById', async (userId, thunkApi) => {
  const response = await fetch(`https://reqres.in/api/users/${userId}`, {
    headers: {
      Authorization: `Bearer ${thunkApi.extra.jwt}`,
    },
  })
  return (await response.json()) as MyData
})

If you are performing a request that you know will typically either be a success or have an expected error format, you can pass in a type to rejectValue and return rejectWithValue(knownPayload) in the action creator. This allows you to reference the error payload in the reducer as well as in a component after dispatching the createAsyncThunk action.

interface MyKnownError {
  errorMessage: string
  // ...
}
interface UserAttributes {
  id: string
  first_name: string
  last_name: string
  email: string
}

const updateUser = createAsyncThunk<
  // Return type of the payload creator
  MyData,
  // First argument to the payload creator
  UserAttributes,
  // Types for ThunkAPI
  {
    extra: {
      jwt: string
    }
    rejectValue: MyKnownError
  }
>('users/update', async (user, thunkApi) => {
  const { id, ...userData } = user
  const response = await fetch(`https://reqres.in/api/users/${id}`, {
    method: 'PUT',
    headers: {
      Authorization: `Bearer ${thunkApi.extra.jwt}`,
    },
    body: JSON.stringify(userData),
  })
  if (response.status === 400) {
    // Return the known error for future handling
    return thunkApi.rejectWithValue((await response.json()) as MyKnownError)
  }
  return (await response.json()) as MyData
})

While this notation for state, dispatch, extra and rejectValue might seem uncommon at first, it allows you to provide only the types for these you actually need - so for example, if you are not accessing getState within your payloadCreator, there is no need to provide a type for state. The same can be said about rejectValue - if you don't need to access any potential error payload, you can ignore it.

In addition, you can leverage checks against action.payload and match as provided by createAction as a type-guard for when you want to access known properties on defined types. Example:

In a reducer

const usersSlice = createSlice({
  name: 'users',
  initialState: {
    entities: {},
    error: null,
  },
  reducers: {},
  extraReducers: (builder) => {
    builder.addCase(updateUser.fulfilled, (state, { payload }) => {
      state.entities[payload.id] = payload
    })
    builder.addCase(updateUser.rejected, (state, action) => {
      if (action.payload) {
        // Since we passed in `MyKnownError` to `rejectValue` in `updateUser`, the type information will be available here.
        state.error = action.payload.errorMessage
      } else {
        state.error = action.error
      }
    })
  },
})

In a component

const handleUpdateUser = async (userData) => {
  const resultAction = await dispatch(updateUser(userData))
  if (updateUser.fulfilled.match(resultAction)) {
    const user = resultAction.payload
    showToast('success', `Updated ${user.name}`)
  } else {
    if (resultAction.payload) {
      // Since we passed in `MyKnownError` to `rejectValue` in `updateUser`, the type information will be available here.
      // Note: this would also be a good place to do any handling that relies on the `rejectedWithValue` payload, such as setting field errors
      showToast('error', `Update failed: ${resultAction.payload.errorMessage}`)
    } else {
      showToast('error', `Update failed: ${resultAction.error.message}`)
    }
  }
}

Defining a Pre-Typed `createAsyncThunk`

As of RTK 1.9, you can define a "pre-typed" version of createAsyncThunk that can have the types for state, dispatch, and extra built in. This lets you set up those types once, so you don't have to repeat them each time you call createAsyncThunk.

To do this, call createAsyncThunk.withTypes<>(), and pass in an object containing the field names and types for any of the fields in the AsyncThunkConfig type listed above. This might look like:

const createAppAsyncThunk = createAsyncThunk.withTypes<{
  state: RootState
  dispatch: AppDispatch
  rejectValue: string
  extra: { s: string; n: number }
}>()

Import and use that pre-typed createAppAsyncThunk instead of the original, and the types will be used automatically.

`createEntityAdapter`

Typing createEntityAdapter only requires you to specify the entity type as the single generic argument.

The example from the createEntityAdapter documentation would look like this in TypeScript:

interface Book {
  bookId: number
  title: string
  // ...
}

const booksAdapter = createEntityAdapter<Book>({
  selectId: (book) => book.bookId,
  sortComparer: (a, b) => a.title.localeCompare(b.title),
})

const booksSlice = createSlice({
  name: 'books',
  initialState: booksAdapter.getInitialState(),
  reducers: {
    bookAdded: booksAdapter.addOne,
    booksReceived(state, action: PayloadAction<{ books: Book[] }>) {
      booksAdapter.setAll(state, action.payload.books)
    },
  },
})

Using `createEntityAdapter` with `normalizr`

When using a library like normalizr, your normalized data will resemble this shape:

{
  result: 1,
  entities: {
    1: { id: 1, other: 'property' },
    2: { id: 2, other: 'property' }
  }
}

The methods addMany, upsertMany, and setAll all allow you to pass in the entities portion of this directly with no extra conversion steps. However, the normalizr TS typings currently do not correctly reflect that multiple data types may be included in the results, so you will need to specify that type structure yourself.

Here is an example of how that would look:

type Author = { id: number; name: string }
type Article = { id: number; title: string }
type Comment = { id: number; commenter: number }

export const fetchArticle = createAsyncThunk(
  'articles/fetchArticle',
  async (id: number) => {
    const data = await fakeAPI.articles.show(id)
    // Normalize the data so reducers can responded to a predictable payload.
    // Note: at the time of writing, normalizr does not automatically infer the result,
    // so we explicitly declare the shape of the returned normalized data as a generic arg.
    const normalized = normalize<
      any,
      {
        articles: { [key: string]: Article }
        users: { [key: string]: Author }
        comments: { [key: string]: Comment }
      }
    >(data, articleEntity)
    return normalized.entities
  }
)

export const slice = createSlice({
  name: 'articles',
  initialState: articlesAdapter.getInitialState(),
  reducers: {},
  extraReducers: (builder) => {
    builder.addCase(fetchArticle.fulfilled, (state, action) => {
      // The type signature on action.payload matches what we passed into the generic for `normalize`, allowing us to access specific properties on `payload.articles` if desired
      articlesAdapter.upsertMany(state, action.payload.articles)
    })
  },
})

Usage With TypeScript

Introduction​

configureStore​

Getting the State type​

Getting the Dispatch type​

Correct typings for the Dispatch type​

Using Tuple without getDefaultMiddleware​

Using the extracted Dispatch type with React Redux​

createAction​

Alternative to using a literally-typed action.type​

createReducer​

Building Type-Safe Reducer Argument Objects​

Typing builder.addMatcher​

createSlice​

Defining the Initial State Type​

Defining Action Contents with prepare Callbacks​

Generated Action Types for Slices​

Type safety with extraReducers​

Payload with All Optional Fields​

Typing Async Thunks Inside createSlice​

Wrapping createSlice​

createAsyncThunk​

Basic createAsyncThunk Types​

Typing the thunkApi Object​

Manually Defining thunkApi Types​

Defining a Pre-Typed createAsyncThunk​

createEntityAdapter​

Using createEntityAdapter with normalizr​