typescript 58 lines · 9 steps

A cancellable polling helper in TypeScript

A generic pollUntil repeatedly fetches until a condition holds, respecting a timeout and an AbortSignal.

Explained by highlit

Intermediate polling async-await abortsignal generics timeout

1interface PollOptions<T> {
2  intervalMs?: number;
3  timeoutMs?: number;
4  signal?: AbortSignal;
5}
6 
7export async function pollUntil<T>(
8  fetchFn: () => Promise<T>,
9  isDone: (value: T) => boolean,
10  { intervalMs = 2000, timeoutMs = 60000, signal }: PollOptions<T> = {},
11): Promise<T> {
12  const deadline = Date.now() + timeoutMs;
13 
14  while (true) {
15    if (signal?.aborted) {
16      throw new DOMException("Polling aborted", "AbortError");
17    }
18 
19    const value = await fetchFn();
20    if (isDone(value)) {
21      return value;
22    }
23 
24    if (Date.now() + intervalMs >= deadline) {
25      throw new Error(`Condition not met within ${timeoutMs}ms`);
26    }
27 
28    await delay(intervalMs, signal);
29  }
30}
31 
32function delay(ms: number, signal?: AbortSignal): Promise<void> {
33  return new Promise((resolve, reject) => {
34    const timer = setTimeout(() => {
35      signal?.removeEventListener("abort", onAbort);
36      resolve();
37    }, ms);
38 
39    const onAbort = () => {
40      clearTimeout(timer);
41      reject(new DOMException("Polling aborted", "AbortError"));
42    };
43 
44    signal?.addEventListener("abort", onAbort, { once: true });
45  });
46}
47 
48export async function waitForJob(jobId: string): Promise<Job> {
49  return pollUntil(
50    async () => {
51      const res = await fetch(`/api/jobs/${jobId}`);
52      if (!res.ok) throw new Error(`Job fetch failed: ${res.status}`);
53      return (await res.json()) as Job;
54    },
55    (job) => job.status === "completed" || job.status === "failed",
56    { intervalMs: 1500, timeoutMs: 120000 },
57  );
58}

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Generics let one polling loop serve any fetch shape while keeping return types precise.
2Wrapping setTimeout in a promise that also listens for abort makes delays cleanly cancellable.
3Checking the deadline before sleeping avoids waiting out a full interval you know will exceed the budget.

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