katanakit-js / MutationObserver

Class: MutationObserver<TData, TError, TVariables, TOnMutateResult>

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:478

Observes a single mutation and derives a MutationObserverResult from it. A framework hook like useMutation creates one MutationObserver per hook call, keeps it stable across re-renders, calls setOptions when the options passed to the hook change, subscribes to it to re-render on updates, and reads getCurrentResult() for the value to return. Calling mutate() builds a new underlying Mutation in the MutationCache and executes it.

Example

const observer = new MutationObserver(queryClient, {
  mutationFn: (variables: { title: string }) => addPost(variables),
})

Extends

• Subscribable<MutationObserverListener<TData, TError, TVariables, TOnMutateResult>>

Type Parameters

Type Parameter	Default type
TData	unknown
TError	DefaultError
TVariables	void
TOnMutateResult	unknown

Constructors

Constructor

new MutationObserver<TData, TError, TVariables, TOnMutateResult>(client, options): MutationObserver<TData, TError, TVariables, TOnMutateResult>;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:481

Parameters

Parameter	Type
client	QueryClient
options	MutationObserverOptions<TData, TError, TVariables, TOnMutateResult>

Returns

MutationObserver<TData, TError, TVariables, TOnMutateResult>

Overrides

Subscribable<MutationObserverListener<TData, TError, TVariables, TOnMutateResult>>.constructor

Properties

Property	Modifier	Type	Inherited from	Defined in
listeners	protected	Set<MutationObserverListener<TData, TError, TVariables, TOnMutateResult>>	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	MutationObserverOptions<TData, TError, TVariables, TOnMutateResult>	-	node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:480

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:482

Returns

void

---

getCurrentResult()

getCurrentResult(): MutationObserverResult<TData, TError, TVariables, TOnMutateResult>;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:509

Returns the observer's current result, derived from the observed mutation's state (or the default, idle state if no mutation has been built yet, e.g. before the first mutate() call or after reset()).

Returns

MutationObserverResult<TData, TError, TVariables, TOnMutateResult>

---

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

---

mutate()

mutate(variables, options?): Promise<TData>;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:545

Builds a new Mutation in the MutationCache using the observer's current options, detaches this observer from any previously observed mutation, attaches it to the new one, and executes it with the given variables.

The optional per-call options (onSuccess/onError/onSettled) are invoked once the mutation settles, in addition to any callbacks defined on the observer's own options.

Parameters

Parameter	Type
variables	TVariables
options?	MutateOptions<TData, TError, TVariables, TOnMutateResult>

Returns

Promise<TData>

Example

await observer.mutate(
  { title: 'New post' },
  { onSuccess: (data) => console.log(data) },
)

---

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:500

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:501

Returns

void

Overrides

Subscribable.onUnsubscribe

---

reset()

reset(): void;

Defined in: node_modules/.bun/@tanstack+query-core@5.104.1/node_modules/@tanstack/query-core/build/modern/hydration-B9t5w6NC.d.ts:526

Detaches the observer from the mutation it is currently observing (if any) and resets the observed result back to its default, idle state.

This does not cancel an in-flight mutation; the mutation itself keeps running to completion and its own callbacks still fire, but this observer stops reflecting its state and a subsequent mutate() call will build a brand new mutation.

Returns

void

Example

observer.reset()

See

MutationObserver#mutate

---

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:499

Updates the observer's options.

If the new mutationKey differs from the previous one (and both were defined), the observer is reset, detaching it from the mutation it was observing. Otherwise, if the currently observed mutation is still pending, its options are updated in place as well.

Parameters

Parameter	Type
options	MutationObserverOptions<TData, TError, TVariables, TOnMutateResult>

Returns

void

Example

observer.setOptions({
  mutationFn: (variables: { title: string }) => addPost(variables),
  onSuccess: (data) => console.log(data),
})

---

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	MutationObserverListener	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