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 v3.8 or greater
- for useQueries, TypeScript v4.1 or greater is required to get the correct return type for each individual query (below v4.1 will mean the type of each returned data property is left as unknown)
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.

Defining Custom Hooks

When defining a custom hook you need to specify the result and error types, for example:

1 function useGroups() {
2   return useQuery<Group[], Error>('groups', fetchGroups)
3 }