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onSnapshot() function

Attaches a listener for QuerySnapshot events. You may either pass individual onNext and onError callbacks or pass a single observer object with next and error callbacks. The listener can be cancelled by calling the function that is returned when onSnapshot is called.

NOTE: Although an onCompletion callback can be provided, it will never be called because the snapshot stream is never-ending.

Signature:

export declare function onSnapshot<T>(query: Query<T>, options: SnapshotListenOptions, observer: {
    next?: (snapshot: QuerySnapshot<T>) => void;
    error?: (error: FirestoreError) => void;
    complete?: () => void;
}): Unsubscribe;

Parameters

Parameter	Type	Description
query	Query<T>	The query to listen to.
options	SnapshotListenOptions	Options controlling the listen behavior.
observer	{ next?: (snapshot: QuerySnapshot<T>) => void; error?: (error: FirestoreError) => void; complete?: () => void; }	A single object containing next and error callbacks.

Returns:

Unsubscribe

An unsubscribe function that can be called to cancel the snapshot listener.