Usage With TypeScript

Usage With TypeScript

:::tip 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({})
// highlight-start
export type RootState = ReturnType<typeof rootReducer>
// highlight-end

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

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,
})

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

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 MiddlewareArray returned by getDefaultMiddleware().

Also, we suggest using the callback notation for the middleware option to get a correctly pre-typed version of getDefaultMiddleware that does not require you to specify any generics by hand.

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,
  // highlight-start
  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),
  // highlight-end
})

export type AppDispatch = typeof store.dispatch

export default store

Using MiddlewareArray without getDefaultMiddleware

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

This is generally not required though, as you will probably not run into any array-type-widening issues as long as you are using as const and do not use the spread operator.

So the following two calls would be equivalent:

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

configureStore({
  reducer: rootReducer,
  middleware: new MiddlewareArray().concat(additionalMiddleware, logger),
})

configureStore({
  reducer: rootReducer,
  middleware: [additionalMiddleware, logger] as const,
})

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

The default way of calling createReducer would be with a "lookup table" / "map object", like this:

createReducer(0, {
  increment: (state, action: PayloadAction<number>) => state + action.payload,
})

Unfortunately, as the keys are only strings, using that API TypeScript can neither infer nor validate the action types for you:

{
  const increment = createAction<number, 'increment'>('increment')
  const decrement = createAction<number, 'decrement'>('decrement')
  createReducer(0, {
    [increment.type]: (state, action) => {
      // action is any here
    },
    [decrement.type]: (state, action: PayloadAction<string>) => {
      // even though action should actually be PayloadAction<number>, TypeScript can't detect that and won't give a warning here.
    },
  })
}

As an alternative, RTK includes a type-safe reducer builder API.

Building Type-Safe Reducer Argument Objects

Instead of using a simple object as an argument to createReducer, you can also use 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
    })
)

We recommend using this API if stricter type safety is necessary when defining reducer argument objects.

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: AnyAction): 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

As TS cannot combine two string literals (slice.name and the key of actionMap) into a new literal, all actionCreators created by createSlice are of type 'string'. This is usually not a problem, as these types are only rarely used as literals.

In most cases that type would be required as a literal, the slice.action.myAction.match type predicate should be a viable alternative:

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

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 may also 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.

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

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',
  // highlight-start
  // Declare the type your function argument here:
  async (userId: number) => {
    // highlight-end
    const response = await fetch(`https://reqres.in/api/users/${userId}`)
    // Inferred return type: Promise<MyData>
    // highlight-next-line
    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))

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.

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<
  // highlight-start
  // 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
    }
  }
  // highlight-end
>('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}`)
    }
  }
}

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
  // ...
}

// highlight-next-line
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)
    })
  },
})