typescript.md

id	title
typescript	TypeScript

React Query is now written in TypeScript to make sure the library and your projects are type-safe!

Things to keep in mind:

• Types currently require using TypeScript v4.7 or greater
• Changes to types in this repository are considered non-breaking and are usually released as patch semver changes (otherwise every type enhancement would be a major version!).
• It is highly recommended that you lock your react-query package version to a specific patch release and upgrade with the expectation that types may be fixed or upgraded between any release
• The non-type-related public API of React Query still follows semver very strictly.

Type Inference

Types in React Query generally flow through very well so that you don't have to provide type annotations for yourself

const { data } = useQuery({
  //    ^? const data: number | undefined
  queryKey: ['test'],
  queryFn: () => Promise.resolve(5),
})

typescript playground

const { data } = useQuery({
  //      ^? const data: string | undefined
  queryKey: ['test'],
  queryFn: () => Promise.resolve(5),
  select: (data) => data.toString(),
})

typescript playground

This works best if your queryFn has a well-defined returned type. Keep in mind that most data fetching libraries return any per default, so make sure to extract it to a properly typed function:

const fetchGroups = (): Promise<Group[]> =>
  axios.get('/groups').then((response) => response.data)

const { data } = useQuery({ queryKey: ['groups'], queryFn: fetchGroups })
//      ^? const data: Group[] | undefined

typescript playground

Type Narrowing

React Query uses a discriminated union type for the query result, discriminated by the status field and the derived status boolean flags. This will allow you to check for e.g. success status to make data defined:

const { data, isSuccess } = useQuery({
  queryKey: ['test'],
  queryFn: () => Promise.resolve(5),
})

if (isSuccess) {
  data
  //  ^? const data: number
}

typescript playground

Typing the error field

The type for error defaults to Error, because that is what most users expect.

const { error } = useQuery({ queryKey: ['groups'], queryFn: fetchGroups })
//      ^? const error: Error

typescript playground

If you want to throw a custom error, or something that isn't an Error at all, you can specify the type of the error field:

const { error } = useQuery<Group[], string>(['groups'], fetchGroups)
//      ^? const error: string | null

However, this has the drawback that type inference for all other generics of useQuery will not work anymore. It is generally not considered a good practice to throw something that isn't an Error, so if you have a subclass like AxiosError you can use type narrowing to make the error field more specific:

import axios from 'axios'

const { error } = useQuery({ queryKey: ['groups'], queryFn: fetchGroups })
//      ^? const error: Error | null

if (axios.isAxiosError(error)) {
  error
  // ^? const error: AxiosError
}

typescript playground

Registering a global Error

TanStack Query v5 allows for a way to set a global Error type for everything, without having to specify generics on call-sides, by amending the Register interface. This will make sure inference still works, but the error field will be of the specified type:

import '@tanstack/react-query'

declare module '@tanstack/react-query' {
  interface Register {
    defaultError: AxiosError
  }
}

const { error } = useQuery({ queryKey: ['groups'], queryFn: fetchGroups })
//      ^? const error: AxiosError | null

Typing meta

Registering global Meta

Similarly to registering a global error type you can also register a global Meta type. This ensures the optional meta field on queries and mutations stays consistent and is type-safe.

import '@tanstack/react-query'

declare module '@tanstack/react-query' {
  interface Register {
    queryMeta: MyMeta
    mutationMeta: MyMeta
  }
}

Typing Query Options

If you inline query options into useQuery, you'll get automatic type inference. However, you might want to extract the query options into a separate function to share them between useQuery and e.g. prefetchQuery. In that case, you'd lose type inference. To get it back, you can use queryOptions helper:

import { queryOptions } from '@tanstack/react-query'

function groupOptions() {
  return queryOptions({
    queryKey: ['groups'],
    queryFn: fetchGroups,
    staleTime: 5 * 1000,
  })
}

useQuery(groupOptions())
queryClient.prefetchQuery(groupOptions())

Further, the queryKey returned from queryOptions knows about the queryFn associated with it, and we can leverage that type information to make functions like queryClient.getQueryData aware of those types as well:

function groupOptions() {
  return queryOptions({
    queryKey: ['groups'],
    queryFn: fetchGroups,
    staleTime: 5 * 1000,
  })
}

const data = queryClient.getQueryData(groupOptions().queryKey)
//     ^? const data: Group[] | undefined

Without queryOptions, the type of data would be unknown, unless we'd pass a generic to it:

const data = queryClient.getQueryData<Group[]>(['groups'])

Further Reading

For tips and tricks around type inference, have a look at React Query and TypeScript from the Community Resources. To find out how to get the best possible type-safety, you can read Type-safe React Query.