React Query is now written in TypeScript to make sure the library and your projects are type-safe!
Things to keep in mind:
Types in React Query generally flow through very well so that you don't have to provide type annotations for yourself
'TypeInference1'
const { data } = useQuery({
// ^? const data: number | undefined
queryKey: ['test'],
queryFn: () => Promise.resolve(5),
})const { data } = useQuery({
// ^? const data: number | undefined
queryKey: ['test'],
queryFn: () => Promise.resolve(5),
})'TypeInference1' 'TypeInference2'
const { data } = useQuery({
// ^? const data: string | undefined
queryKey: ['test'],
queryFn: () => Promise.resolve(5),
select: (data) => data.toString(),
})const { data } = useQuery({
// ^? const data: string | undefined
queryKey: ['test'],
queryFn: () => Promise.resolve(5),
select: (data) => data.toString(),
})'TypeInference2'
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:
'TypeInference3'
const fetchGroups = (): Promise<Group[]> =>
axios.get('/groups').then((response) => response.data)
const { data } = useQuery({ queryKey: ['groups'], queryFn: fetchGroups })
// ^? const data: Group[] | undefinedconst fetchGroups = (): Promise<Group[]> =>
axios.get('/groups').then((response) => response.data)
const { data } = useQuery({ queryKey: ['groups'], queryFn: fetchGroups })
// ^? const data: Group[] | undefined'TypeInference3'
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:
'TypeNarrowing'
const { data, isSuccess } = useQuery({
queryKey: ['test'],
queryFn: () => Promise.resolve(5),
})
if (isSuccess) {
data
// ^? const data: number
}const { data, isSuccess } = useQuery({
queryKey: ['test'],
queryFn: () => Promise.resolve(5),
})
if (isSuccess) {
data
// ^? const data: number
}'TypeNarrowing'
The type for error defaults to unknown. This is in line with what TypeScript gives you per default in a catch clauses (see useUnknownInCatchVariables). The safest way to work with error would be to perform a runtime check; another way would be to explicitly define types for data and error:
'TypingError'
const { error } = useQuery({ queryKey: ['groups'], queryFn: fetchGroups })
// ^? const error: unknown
if (error instanceof Error) {
error
// ^? const error: Error
}const { error } = useQuery({ queryKey: ['groups'], queryFn: fetchGroups })
// ^? const error: unknown
if (error instanceof Error) {
error
// ^? const error: Error
}'TypingError' 'TypingError2'
const { error } = useQuery<Group[], Error>(['groups'], fetchGroups)
// ^? const error: Error | nullconst { error } = useQuery<Group[], Error>(['groups'], fetchGroups)
// ^? const error: Error | null'TypingError2' 'Materials'
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.
'Materials' 'Materials'
“This course is the best way to learn how to use React Query in real-world applications.”—Tanner LinsleyCheck it out