Using React Query v4 together with React v17

[bennettdams]

I know that React Query v4 now comes with first-class support for React v18, it is also mentioned in the migration guide.
But how does v4 work with React v17? Isn't v4 using useSyncExternalStore, which only exists for React v18?

The v4 still has React v17 as a valid peer dependency - are there now two "implementations" in v4, one with and one without useSyncExternalStore?
What are the differences of using v4 with React v17 vs. v18? Also keeping in mind Suspense etc.

[TkDodo]

We are using the use-sync-external-store shim provided by react. It uses the new hook if available and falls back to an implementation with useEffect for v17. other libs like redux do the same afaik.

query/packages/react-query/package.json

Line 51 in 3932866

"use-sync-external-store": "^1.2.0"

We run our tests both against v17 and v18, so both are fully supported.