Topic
Definition
TanStack Query manages asynchronous server state through query keys, query functions, caching, invalidation, and mutation lifecycles.
In simpler words
Give server data a stable cache identity and let Query handle loading, errors, refetching, and stale data.
useQuery, useMutation, query keys, and invalidation.
useQuery, useMutation, query keys, and invalidation.
Start by identifying which value or browser behavior changes. Then describe the UI from that current input instead of editing the DOM as a separate source of truth.
const ticketsQuery = useQuery({
queryKey: ["tickets", { status }],
queryFn: () => ticketsApi.list({ status }),
});Read the example from data and control flow to the resulting UI. Keep the component boundary small.
Keep rendering as a calculation. Put user-triggered changes in event handlers, preserve UI memory in state, and reserve external synchronization for Effects or the server-state layer.
Name values by their UI meaning, test the loading and error path when data is remote, and avoid keeping two editable copies of the same value.
Ask before adding code: is this local UI memory, shared client state, or Nest-owned server state?
Definition
High-bug areas are places where a small API misuse looks correct but produces stale UI, duplicate work, or silent failures.
In simpler words
Each mistake below shows Wrong vs Right code — compare them side by side.
When something misbehaves, match the symptom to a pattern below before rewriting the feature.
Prefer fixing the ownership or update path over adding another Effect or sync step.
// Wrong
useQuery({ queryKey: ["t", { status }], queryFn })
// new filter object identity every parent render without memo
// Right
useQuery({ queryKey: ["t", status], queryFn })Prefer stable key parts.
// Wrong
await create(dto);
// list stays stale
// Right
await create(dto);
queryClient.invalidateQueries({ queryKey: ["tickets"] });Refresh the server cache after writes.
// Wrong
useQuery({ queryKey: ["draft"], queryFn: () => localDraft })
// Right
// RTK / useState for drafts; Query for Nest dataClient-only drafts are not server state.
Live playground
Change one input at a time and predict the next render.
Different keys → different cache entries.
Test
At least 10 questions — mix of concept, syntax, practical, and logic. Score ≥ 80% (enforced by the API) to save progress.
Checking your session…
10 questions · concept 3 · syntax 3 · practical 2 · logic 2