fromAbortablePromise

Creates an observable from a Promise factory that receives an AbortSignal. When the observable is completed (e.g., by switchMap switching to a new inner observable), the AbortController is automatically aborted, cancelling the in-flight request.

Emits Result.ok(value) when the promise resolves, or Result.err(error) when it rejects. Rejections caused by abort (AbortError) are silently ignored and do not emit.

Example

//  Timeline:
//
//  query$      "a"            "b"
//  request a   [in flight]    | (aborted)
//  request b                  [in flight]  -> "result for b"
//  results$                                  Ok("result for b")
//
//  Explanation:
//  - fromAbortablePromise hands its factory an AbortSignal
//  - switchMap completes the previous inner observable, which aborts it
//  - The AbortError that follows is swallowed, so nothing is emitted for it

const search = (query: string, signal: AbortSignal): Promise<string> =>
    new Promise((resolve, reject) => {
        const timer = setTimeout(() => {
            resolve(`result for ${query}`);
        }, 50);

        signal.addEventListener('abort', () => {
            clearTimeout(timer);

            reject(new DOMException('aborted', 'AbortError'));
        });
    });

const query$ = source<string>();

const results$ = query$.pipe(
    switchMap((query) =>
        fromAbortablePromise((signal) => search(query, signal)),
    ),
);

const valueHistory: Result<string, unknown>[] = [];

results$.subscribe((result) => {
    valueHistory.push(result);
});

query$.next('a');

query$.next('b');

await new Promise<void>((resolve) => {
    setTimeout(resolve, 150);
});

assert.deepStrictEqual(valueHistory, [Result.ok('result for b')]);

Use it instead of fromPromise when the request can be cancelled, typically as the projection of switchMap, so that a request whose answer nobody waits for any longer is aborted rather than left running.

View source on GitHub