firstValueFrom()

Subscribes to a raw callbag source and resolves with the first value matching the optional predicate. Pure callbag — no Store dependency.

For Store objects (which need a .get() fast path), use extra/firstValueFrom.

This is the canonical callbag → Promise bridge. Business logic should use this instead of new Promise.

Signature

function firstValueFrom<T>(
	source: CallbagSource,
	opts?: { predicate?: (value: T) => boolean; signal?: AbortSignal },
): Promise<T>

Parameters

Parameter	Type	Description
source	CallbagSource	A raw callbag source function.
opts	{ predicate?: (value: T) => boolean; signal?: AbortSignal }	Optional predicate filter and/or AbortSignal for cancellation.

Returns

Promise that resolves with the matching value, or rejects if the source completes (END) without a match or the signal is aborted.

Options / Behavior Details

• If the source never emits and no signal is provided, the returned Promise never settles and the subscription is never cleaned up. Always pass signal when subscribing to potentially non-completing sources.