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 v4.1 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.

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 }