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Usage With TypeScript

What You'll Learn
  • Details on how to use various RTK Query APIs with TypeScript

Introduction​

As with the rest of the Redux Toolkit package, RTK Query is written in TypeScript, and its API is designed for seamless use in TypeScript applications.

This page provides details for using APIs included in RTK Query with TypeScript and how to type them correctly.

info

We strongly recommend using TypeScript 4.1+ with RTK Query for best results.

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

createApi​

Using auto-generated React Hooks​

The React-specific entry point for RTK Query exports a version of createApi which automatically generates React hooks for each of the defined query & mutation endpoints.

To use the auto-generated React Hooks as a TypeScript user, you'll need to use TS4.1+.

// Need to use the React-specific entry point to allow generating React hooks
import { createApi, fetchBaseQuery } from '@reduxjs/toolkit/query/react'
import type { Pokemon } from './types'

// Define a service using a base URL and expected endpoints
export const pokemonApi = createApi({
  reducerPath: 'pokemonApi',
  baseQuery: fetchBaseQuery({ baseUrl: 'https://pokeapi.co/api/v2/' }),
  endpoints: (builder) => ({
    getPokemonByName: builder.query<Pokemon, string>({
      query: (name) => `pokemon/${name}`,
    }),
  }),
})

// Export hooks for usage in function components, which are
// auto-generated based on the defined endpoints
export const { useGetPokemonByNameQuery } = pokemonApi

For older versions of TS, you can use api.endpoints.[endpointName].useQuery/useMutation to access the same hooks.

Accessing api hooks directly
import { pokemonApi } from './pokemon'

const useGetPokemonByNameQuery = pokemonApi.endpoints.getPokemonByName.useQuery

Typing a baseQuery​

Typing a custom baseQuery can be done using the BaseQueryFn type exported by RTK Query.

Base Query signature
export type BaseQueryFn<
  Args = any,
  Result = unknown,
  Error = unknown,
  DefinitionExtraOptions = {},
  Meta = {}
> = (
  args: Args,
  api: BaseQueryApi,
  extraOptions: DefinitionExtraOptions
) => MaybePromise<QueryReturnValue<Result, Error, Meta>>

export interface BaseQueryApi {
  signal: AbortSignal
  dispatch: ThunkDispatch<any, any, any>
  getState: () => unknown
}

export type QueryReturnValue<T = unknown, E = unknown, M = unknown> =
  | {
      error: E
      data?: undefined
      meta?: M
    }
  | {
      error?: undefined
      data: T
      meta?: M
    }

The BaseQueryFn type accepts the following generics:

  • Args - The type for the first parameter of the function. The result returned by a query property on an endpoint will be passed here.
  • Result - The type to be returned in the data property for the success case. Unless you expect all queries and mutations to return the same type, it is recommended to keep this typed as unknown, and specify the types individually as shown below.
  • Error - The type to be returned for the error property in the error case. This type also applies to all queryFn functions used in endpoints throughout the API definition.
  • DefinitionExtraOptions - The type for the third parameter of the function. The value provided to the extraOptions property on an endpoint will be passed here.
  • Meta - the type of the meta property that may be returned from calling the baseQuery. The meta property is accessible as the second argument to transformResponse.
note

The meta property returned from a baseQuery will always be considered as potentially undefined, as a throw in the error case may result in it not being provided. When accessing values from the meta property, this should be accounted for, e.g. using optional chaining

Simple baseQuery TypeScript example
import { createApi } from '@reduxjs/toolkit/query'
import type { BaseQueryFn } from '@reduxjs/toolkit/query'

const simpleBaseQuery: BaseQueryFn<
  string, // Args
  unknown, // Result
  { reason: string }, // Error
  { shout?: boolean }, // DefinitionExtraOptions
  { timestamp: number } // Meta
> = (arg, api, extraOptions) => {
  // `arg` has the type `string`
  // `api` has the type `BaseQueryApi` (not configurable)
  // `extraOptions` has the type `{ shout?: boolean }

  const meta = { timestamp: Date.now() }

  if (arg === 'forceFail') {
    return {
      error: {
        reason: 'Intentionally requested to fail!',
        meta,
      },
    }
  }

  if (extraOptions.shout) {
    return { data: 'CONGRATULATIONS', meta }
  }

  return { data: 'congratulations', meta }
}

const api = createApi({
  baseQuery: simpleBaseQuery,
  endpoints: (builder) => ({
    getSupport: builder.query({
      query: () => 'support me',
      extraOptions: {
        shout: true,
      },
    }),
  }),
})

Typing query and mutation endpoints​

endpoints for an api are defined as an object using the builder syntax. Both query and mutation endpoints can be typed by providing types to the generics in <ResultType, QueryArg> format.

  • ResultType - The type of the final data returned by the query, factoring an optional transformResponse.
    • If transformResponse is not provided, then it is treated as though a successful query will return this type instead.
    • If transformResponse is provided, the input type for transformResponse must also be specified, to indicate the type that the initial query returns. The return type for transformResponse must match ResultType.
    • If queryFn is used rather than query, then it must return the following shape for the success case:
      {
        data: ResultType
      }
  • QueryArg - The type of the input that will be passed as the only parameter to the query property of the endpoint, or the first parameter of a queryFn property if used instead.
    • If query doesn't have a parameter, then void type has to be provided explicitly.
    • If query has an optional parameter, then a union type with the type of parameter, and void has to be provided, e.g. number | void.
Defining endpoints with TypeScript
import { createApi, fetchBaseQuery } from '@reduxjs/toolkit/query/react'
interface Post {
  id: number
  name: string
}

const api = createApi({
  baseQuery: fetchBaseQuery({ baseUrl: '/' }),
  endpoints: (build) => ({
    //              ResultType  QueryArg
    //                    v       v
    getPost: build.query<Post, number>({
      // inferred as `number` from the `QueryArg` type
      //       v
      query: (id) => `post/${id}`,
      // An explicit type must be provided to the raw result that the query returns
      // when using `transformResponse`
      //                             v
      transformResponse: (rawResult: { result: { post: Post } }, meta) => {
        //                                                        ^
        // The optional `meta` property is available based on the type for the `baseQuery` used

        // The return value for `transformResponse` must match `ResultType`
        return rawResult.result.post
      },
    }),
  }),
})
note

queries and mutations can also have their return type defined by a baseQuery rather than the method shown above, however, unless you expect all of your queries and mutations to return the same type, it is recommended to leave the return type of the baseQuery as unknown.

Typing a queryFn​

As mentioned in Typing query and mutation endpoints, a queryFn will receive its result & arg types from the generics provided to the corresponding built endpoint.

import { createApi, fetchBaseQuery } from '@reduxjs/toolkit/query/react'
import { getRandomName } from './randomData'

interface Post {
  id: number
  name: string
}

const api = createApi({
  baseQuery: fetchBaseQuery({ baseUrl: '/' }),
  endpoints: (build) => ({
    //              ResultType  QueryArg
    //                    v       v
    getPost: build.query<Post, number>({
      // inferred as `number` from the `QueryArg` type
      //         v
      queryFn: (arg, queryApi, extraOptions, baseQuery) => {
        const post: Post = {
          id: arg,
          name: getRandomName(),
        }
        // For the success case, the return type for the `data` property
        // must match `ResultType`
        //              v
        return { data: post }
      },
    }),
  }),
})

The error type that a queryFn must return is determined by the baseQuery provided to createApi.

With fetchBaseQuery, the error type is like so:

fetchBaseQuery error shape
{
  status: number
  data: any
}

An error case for the example above using queryFn and the error type from fetchBaseQuery could look like:

queryFn error example with error type from fetchBaseQuery
import { createApi, fetchBaseQuery } from '@reduxjs/toolkit/query/react'
import { getRandomName } from './randomData'

interface Post {
  id: number
  name: string
}

const api = createApi({
  baseQuery: fetchBaseQuery({ baseUrl: '/' }),
  endpoints: (build) => ({
    getPost: build.query<Post, number>({
      queryFn: (arg, queryApi, extraOptions, baseQuery) => {
        if (arg <= 0) {
          return {
            error: {
              status: 500,
              statusText: 'Internal Server Error',
              data: 'Invalid ID provided.',
            },
          }
        }
        const post: Post = {
          id: arg,
          name: getRandomName(),
        }
        return { data: post }
      },
    }),
  }),
})

For users who wish to only use queryFn for each endpoint and not include a baseQuery at all, RTK Query provides a fakeBaseQuery function that can be used to easily specify the error type each queryFn should return.

Excluding baseQuery for all endpoints
import { createApi, fakeBaseQuery } from '@reduxjs/toolkit/query'

type CustomErrorType = { reason: 'too cold' | 'too hot' }

const api = createApi({
  // This type will be used as the error type for all `queryFn` functions provided
  //                              v
  baseQuery: fakeBaseQuery<CustomErrorType>(),
  endpoints: (build) => ({
    eatPorridge: build.query<'just right', 1 | 2 | 3>({
      queryFn(seat) {
        if (seat === 1) {
          return { error: { reason: 'too cold' } }
        }

        if (seat === 2) {
          return { error: { reason: 'too hot' } }
        }

        return { data: 'just right' }
      },
    }),
    microwaveHotPocket: build.query<'delicious!', number>({
      queryFn(duration) {
        if (duration < 110) {
          return { error: { reason: 'too cold' } }
        }
        if (duration > 140) {
          return { error: { reason: 'too hot' } }
        }

        return { data: 'delicious!' }
      },
    }),
  }),
})

Typing providesTags/invalidatesTags​

RTK Query utilizes a cache tag invalidation system in order to provide automated re-fetching of stale data.

When using the function notation, both the providesTags and invalidatesTags properties on endpoints are called with the following arguments:

  • result: ResultType | undefined - The result returned by a successful query. The type corresponds with ResultType as supplied to the built endpoint. In the error case for a query, this will be undefined.
  • error: ErrorType | undefined - The error returned by an errored query. The type corresponds with Error as supplied to the baseQuery for the api. In the success case for a query, this will be undefined.
  • arg: QueryArg - The argument supplied to the query property when the query itself is called. The type corresponds with QueryArg as supplied to the built endpoint.

A recommended use-case with providesTags when a query returns a list of items is to provide a tag for each item in the list using the entity ID, as well as a 'LIST' ID tag (see Advanced Invalidation with abstract tag IDs).

This is often written by spreading the result of mapping the received data into an array, as well as an additional item in the array for the 'LIST' ID tag. When spreading the mapped array, by default, TypeScript will broaden the type property to string. As the tag type must correspond to one of the string literals provided to the tagTypes property of the api, the broad string type will not satisfy TypeScript. In order to alleviate this, the tag type can be cast as const to prevent the type being broadened to string.

providesTags TypeScript example
import { createApi, fetchBaseQuery } from '@reduxjs/toolkit/query/react'
interface Post {
  id: number
  name: string
}
type PostsResponse = Post[]

const api = createApi({
  baseQuery: fetchBaseQuery({ baseUrl: '/' }),
  tagTypes: ['Posts'],
  endpoints: (build) => ({
    getPosts: build.query<PostsResponse, void>({
      query: () => 'posts',
      providesTags: (result) =>
        result
          ? [
              ...result.map(({ id }) => ({ type: 'Posts' as const, id })),
              { type: 'Posts', id: 'LIST' },
            ]
          : [{ type: 'Posts', id: 'LIST' }],
    }),
  }),
})

Skipping queries with TypeScript using skipToken​

RTK Query provides the ability to conditionally skip queries from automatically running using the skip parameter as part of query hook options (see Conditional Fetching).

TypeScript users may find that they encounter invalid type scenarios when a query argument is typed to not be undefined, and they attempt to skip the query when an argument would not be valid.

API definition
import { createApi, fetchBaseQuery } from '@reduxjs/toolkit/query/react'
import type { Post } from './types'

export const api = createApi({
  baseQuery: fetchBaseQuery({ baseUrl: '/' }),
  endpoints: (build) => ({
    // Query argument is required to be `number`, and can't be `undefined`
    //                            V
    getPost: build.query<Post, number>({
      query: (id) => `post/${id}`,
    }),
  }),
})

export const { useGetPostQuery } = api
Using skip in a component
import { useGetPostQuery } from './api'

function MaybePost({ id }: { id?: number }) {
  // This will produce a typescript error:
  // Argument of type 'number | undefined' is not assignable to parameter of type 'number | unique symbol'.
  // Type 'undefined' is not assignable to type 'number | unique symbol'.

  // @ts-expect-error id passed must be a number, but we don't call it when it isn't a number
  const { data } = useGetPostQuery(id, { skip: !id })

  return <div>...</div>
}

While you might be able to convince yourself that the query won't be called unless the id arg is a number at the time, TypeScript won't be convinced so easily.

RTK Query provides a skipToken export which can be used as an alternative to the skip option in order to skip queries, while remaining type-safe. When skipToken is passed as the query argument to useQuery, useQueryState or useQuerySubscription, it provides the same effect as setting skip: true in the query options, while also being a valid argument in scenarios where the arg might be undefined otherwise.

Using skipToken in a component
import { skipToken } from '@reduxjs/toolkit/query/react'
import { useGetPostQuery } from './api'

function MaybePost({ id }: { id?: number }) {
  // When `id` is nullish, we will still skip the query.
  // TypeScript is also happy that the query will only ever be called with a `number` now
  const { data } = useGetPostQuery(id ?? skipToken)

  return <div>...</div>
}

Type safe error handling​

When an error is gracefully provided from a base query, RTK query will provide the error directly. If an unexpected error is thrown by user code rather than a handled error, that error will be transformed into a SerializedError shape. Users should make sure that they are checking which kind of error they are dealing with before attempting to access its properties. This can be done in a type safe manner either by using a type guard, e.g. by checking for discriminated properties, or using a type predicate.

When using fetchBaseQuery, as your base query, errors will be of type FetchBaseQueryError | SerializedError. The specific shapes of those types can be seen below.

FetchBaseQueryError type
export type FetchBaseQueryError =
  | {
      /**
       * * `number`:
       *   HTTP status code
       */
      status: number
      data: unknown
    }
  | {
      /**
       * * `"FETCH_ERROR"`:
       *   An error that occurred during execution of `fetch` or the `fetchFn` callback option
       **/
      status: 'FETCH_ERROR'
      data?: undefined
      error: string
    }
  | {
      /**
       * * `"PARSING_ERROR"`:
       *   An error happened during parsing.
       *   Most likely a non-JSON-response was returned with the default `responseHandler` "JSON",
       *   or an error occurred while executing a custom `responseHandler`.
       **/
      status: 'PARSING_ERROR'
      originalStatus: number
      data: string
      error: string
    }
  | {
      /**
       * * `"CUSTOM_ERROR"`:
       *   A custom error type that you can return from your `queryFn` where another error might not make sense.
       **/
      status: 'CUSTOM_ERROR'
      data?: unknown
      error: string
    }
SerializedError type
export interface SerializedError {
  name?: string
  message?: string
  stack?: string
  code?: string
}

Error result example​

When using fetchBaseQuery, the error property returned from a hook will have the type FetchBaseQueryError | SerializedError | undefined. If an error is present, you can access error properties after narrowing the type to either FetchBaseQueryError or SerializedError.

import { api } from './services/api'

function PostDetail() {
  const { data, error, isLoading } = usePostsQuery()

  if (isLoading) {
    return <div>Loading...</div>
  }

  if (error) {
    if ('status' in error) {
      // you can access all properties of `FetchBaseQueryError` here
      const errMsg = 'error' in error ? error.error : JSON.stringify(error.data)

      return (
        <div>
          <div>An error has occurred:</div>
          <div>{errMsg}</div>
        </div>
      )
    }
    else {
        // you can access all properties of `SerializedError` here
        return <div>{error.message}</div>
    }
  }

  if (data) {
    return (
      <div>
        {data.map((post) => (
          <div key={post.id}>Name: {post.name}</div>
        ))}
      </div>
    )
  }

  return null
}

Inline error handling example​

When handling errors inline after unwrapping a mutation call, a thrown error will have a type of any for typescript versions below 4.4, or unknown for versions 4.4+. In order to safely access properties of the error, you must first narrow the type to a known type. This can be done using a type predicate as shown below.

services/helpers.ts
import { FetchBaseQueryError } from '@reduxjs/toolkit/query'

/**
 * Type predicate to narrow an unknown error to `FetchBaseQueryError`
 */
export function isFetchBaseQueryError(
  error: unknown
): error is FetchBaseQueryError {
  return typeof error === 'object' && error != null && 'status' in error
}

/**
 * Type predicate to narrow an unknown error to an object with a string 'message' property
 */
export function isErrorWithMessage(
  error: unknown
): error is { message: string } {
  return (
    typeof error === 'object' &&
    error != null &&
    'message' in error &&
    typeof (error as any).message === 'string'
  )
}
addPost.tsx
import { useState } from 'react'
import { useSnackbar } from 'notistack'
import { api } from './services/api'
import { isFetchBaseQueryError, isErrorWithMessage } from './services/helpers'

function AddPost() {
  const { enqueueSnackbar, closeSnackbar } = useSnackbar()
  const [name, setName] = useState('')
  const [addPost] = useAddPostMutation()

  async function handleAddPost() {
    try {
      await addPost(name).unwrap()
      setName('')
    } catch (err) {
      if (isFetchBaseQueryError(err)) {
        // you can access all properties of `FetchBaseQueryError` here
        const errMsg = 'error' in err ? err.error : JSON.stringify(err.data)
        enqueueSnackbar(errMsg, { variant: 'error' })
      } else if (isErrorWithMessage(err)) {
        // you can access a string 'message' property here
        enqueueSnackbar(err.message, { variant: 'error' })
      }
    }
  }

  return (
    <div>
      <input value={name} onChange={(e) => setName(e.target.value)} />
      <button>Add post</button>
    </div>
  )
}
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