katanakit-js / QueryObserver

Class: QueryObserver<TQueryFnData, TError, TData, TQueryData, TQueryKey>

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:28

A QueryObserver watches a single query in the QueryCache and computes a QueryObserverResult from its state, recomputing and notifying subscribers whenever the underlying query (or the observer's options) changes. It is the primitive that framework adapters (e.g. useQuery) build their hooks on top of, but it can also be used directly to observe and switch between queries outside of any framework.

Example

const observer = new QueryObserver(queryClient, {
  queryKey: ['posts'],
  queryFn: fetchPosts,
})

const unsubscribe = observer.subscribe((result) => {
  console.log(result.data)
})

Extends

• Subscribable<QueryObserverListener<TData, TError>>

Extended by

• InfiniteQueryObserver

Type Parameters

Type Parameter	Default type
TQueryFnData	unknown
TError	DefaultError
TData	TQueryFnData
TQueryData	TQueryFnData
TQueryKey extends QueryKey	QueryKey

Constructors

Constructor

new QueryObserver<TQueryFnData, TError, TData, TQueryData, TQueryKey>(client, options): QueryObserver<TQueryFnData, TError, TData, TQueryData, TQueryKey>;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:31

Parameters

Parameter	Type
client	QueryClient
options	QueryObserverOptions<TQueryFnData, TError, TData, TQueryData, TQueryKey>

Returns

QueryObserver<TQueryFnData, TError, TData, TQueryData, TQueryKey>

Overrides

Subscribable<QueryObserverListener<TData, TError>>.constructor

Properties

Property	Modifier	Type	Inherited from	Defined in
listeners	protected	Set<QueryObserverListener<TData, TError>>	Subscribable.listeners	node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/subscribable-CysQ0tne.d.ts:8
options	public	QueryObserverOptions<TQueryFnData, TError, TData, TQueryData, TQueryKey>	-	node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:30

Methods

bindMethods()

protected bindMethods(): void;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:32

Returns

void

---

createResult()

protected createResult(query, options): QueryObserverResult<TData, TError>;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:135

Parameters

Parameter	Type
query	Query<TQueryFnData, TError, TQueryData, TQueryKey>
options	QueryObserverOptions<TQueryFnData, TError, TData, TQueryData, TQueryKey>

Returns

QueryObserverResult<TData, TError>

---

destroy()

destroy(): void;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:52

Stops observing the current query: clears all listeners, cancels the stale and refetch-interval timers, and removes this observer from the query it was observing.

Returns

void

---

fetch()

protected fetch(fetchOptions): Promise<QueryObserverResult<TData, TError>>;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:134

Parameters

Parameter	Type
fetchOptions	ObserverFetchOptions

Returns

Promise<QueryObserverResult<TData, TError>>

---

fetchOptimistic()

fetchOptimistic(options): Promise<QueryObserverResult<TData, TError>>;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:133

Fetches a query defined by the given options without affecting this observer's own tracked query or result, and returns a promise that resolves with the QueryObserverResult for that fetch. This is useful for prefetching data that another observer (e.g. a query about to be navigated to) will need, ahead of time.

Parameters

Parameter	Type
options	QueryObserverOptions<TQueryFnData, TError, TData, TQueryData, TQueryKey>

Returns

Promise<QueryObserverResult<TData, TError>>

Example

const result = await observer.fetchOptimistic({
  queryKey: ['posts', 2],
  queryFn: () => fetchPost(2),
})
console.log(result.data)

---

getCurrentQuery()

getCurrentQuery(): Query<TQueryFnData, TError, TQueryData, TQueryKey>;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:105

Returns the Query instance this observer is currently observing.

Returns

Query<TQueryFnData, TError, TQueryData, TQueryKey>

---

getCurrentResult()

getCurrentResult(): QueryObserverResult<TData, TError>;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:87

Returns the most recently computed QueryObserverResult for the observed query. This is a point-in-time read; to be notified of updates as they happen, subscribe to the observer instead (its inherited subscribe method).

Returns

QueryObserverResult<TData, TError>

Example

const result = observer.getCurrentResult()
console.log(result.status, result.data)

---

getOptimisticResult()

getOptimisticResult(options): QueryObserverResult<TData, TError>;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:74

Computes the result the observer would produce for the given (already-defaulted) options right now, building the underlying Query if it doesn't exist yet, without waiting for a subscription callback. Called by framework adapters on every render (e.g. useQuery) so the returned value is available synchronously, ahead of setOptions triggering an actual fetch.

Parameters

Parameter	Type
options	DefaultedQueryObserverOptions<TQueryFnData, TError, TData, TQueryData, TQueryKey>

Returns

QueryObserverResult<TData, TError>

---

hasListeners()

hasListeners(): boolean;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/subscribable-CysQ0tne.d.ts:28

Returns true while at least one listener is registered, false once they have all unsubscribed.

Returns

boolean

Inherited from

Subscribable.hasListeners

---

onSubscribe()

protected onSubscribe(): void;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:33

Returns

void

Overrides

Subscribable.onSubscribe

---

onUnsubscribe()

protected onUnsubscribe(): void;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:34

Returns

void

Overrides

Subscribable.onUnsubscribe

---

refetch()

refetch(__namedParameters?): Promise<QueryObserverResult<TData, TError>>;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:116

Refetches the observed query and returns a promise that resolves with the resulting QueryObserverResult.

Parameters

Parameter	Type
__namedParameters?	RefetchOptions

Returns

Promise<QueryObserverResult<TData, TError>>

Example

const result = await observer.refetch({ cancelRefetch: false })
console.log(result.data)

---

setOptions()

setOptions(options): void;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:67

Updates the observer's options. This will re-resolve the query being observed (switching to a different query if the queryKey changed), trigger a fetch if the new options require one and the observer has subscribers, recompute the current result, and reschedule the stale and refetch-interval timers as needed.

Parameters

Parameter	Type
options	QueryObserverOptions<TQueryFnData, TError, TData, TQueryData, TQueryKey>

Returns

void

Example

observer.setOptions({ queryKey: ['posts', 1], queryFn: () => fetchPost(1) })
// later: switch to a different query, reusing the same observer
observer.setOptions({ queryKey: ['posts', 2], queryFn: () => fetchPost(2) })

---

shouldFetchOnReconnect()

shouldFetchOnReconnect(): boolean;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:40

Returns whether the observed query is currently stale and configured (via the refetchOnReconnect option) to refetch when the network reconnects.

Returns

boolean

---

shouldFetchOnWindowFocus()

shouldFetchOnWindowFocus(): boolean;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:46

Returns whether the observed query is currently stale and configured (via the refetchOnWindowFocus option) to refetch when the window regains focus.

Returns

boolean

---

subscribe()

subscribe(listener): () => void;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/subscribable-CysQ0tne.d.ts:24

Registers a listener to be called on every update this object notifies about. Returns a function that removes the listener again — call it to stop listening. The base class never drops a listener on its own, though some subclasses clear all of theirs in destroy().

Parameters

Parameter	Type	Description
listener	QueryObserverListener	Called on each update, with whatever the subclass passes to its subscribers.

Returns

() => void

Example

const unsubscribe = subscribable.subscribe(() => {
  // react to the update
})

unsubscribe()

Inherited from

Subscribable.subscribe

---

trackProp()

trackProp(key): void;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:101

Records that the given QueryObserverResult property was read, so a subsequent update only notifies this observer if a tracked property actually changed. Normally called indirectly via QueryObserver#trackResult's proxy; exposed directly for adapters that track property access themselves (e.g. through their own reactivity system) instead of via the proxy.

Parameters

Parameter	Type
key	| "data" | "error" | "status" | "isPending" | "isRefetching" | "refetch" | "isPaused" | "isError" | "isLoading" | "isLoadingError" | "isRefetchError" | "isSuccess" | "isPlaceholderData" | "dataUpdatedAt" | "errorUpdatedAt" | "failureCount" | "failureReason" | "errorUpdateCount" | "isFetched" | "isFetchedAfterMount" | "isFetching" | "isInitialLoading" | "isStale" | "isEnabled" | "fetchStatus"

Returns

void

---

trackResult()

trackResult(result, onPropTracked?): QueryObserverResult<TData, TError>;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:94

Wraps a QueryObserverResult in a Proxy that records which properties are read, via QueryObserver#trackProp (and an optional onPropTracked callback). Used by framework adapters when notifyOnChangeProps is not set, to implement its default "only re-render on properties you actually read" behavior.

Parameters

Parameter	Type
result	QueryObserverResult<TData, TError>
onPropTracked?	(key) => void

Returns

QueryObserverResult<TData, TError>

---

updateResult()

updateResult(): void;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:141

Recomputes and stores the current result from the current query/options, notifying listeners if it changed. Framework adapters call this right after subscribing to make sure no query update was missed in the gap between creating the observer and subscribing to it.

Returns

void