@std/async

Overview Jump to heading#

Provide helpers with asynchronous tasks like delays, debouncing, retrying, or pooling.

import { delay } from "@std/async/delay";

await delay(100); // waits for 100 milliseconds

Add to your project Jump to heading#

deno add jsr:@std/async

See all symbols in @std/async on

What is async? Jump to heading#

Asynchronous programming lets your program start work now and finish it later without blocking the main thread. In JavaScript this typically means Promises, async/await, timers, and async iterables. Async code improves responsiveness and throughput by overlapping I/O (network, disk, timers) and controlling concurrency.

Why use @std/async? Jump to heading#

This package gives you small, focused utilities that solve common async problems so you don’t have to re‑implement them:

• delay and deadline for scheduling and timeouts (with cancellation via AbortSignal).
• debounce (and throttle in unstable) to control call frequency for UI/CLI events.
• retry with backoff/jitter for flaky operations like HTTP requests.
• pooledMap to cap concurrency when transforming streams of work.
• tee/MuxAsyncIterator to branch or merge async iterables.

These helpers are tiny, predictable, and work across Deno, Node.js, Bun, Workers, and the browser.

Examples Jump to heading#

Debounce rapid events (e.g., typeahead):

import { debounce } from "@std/async/debounce";

const search = debounce(async (q: string) => {
  // fetch results after the user pauses typing
}, 200);

// call many times; only the last call after 200ms runs
search("d");
search("de");
search("deno");

Retry with exponential backoff and jitter:

import { retry } from "@std/async/retry";

const data = await retry(() =>
  fetch("/api").then((r) => {
    if (!r.ok) throw new Error("bad status");
    return r.json();
  }), {
  maxAttempts: 5,
  minTimeout: 100,
  multiplier: 2,
  jitter: 0.2,
});

Limit concurrency with pooledMap:

import { pooledMap } from "@std/async/pool";

const urls = ["/a", "/b", "/c", "/d"]; // many more in practice
for await (const res of pooledMap(3, urls, (u) => fetch(u))) {
  // at most 3 fetches in flight; results arrive as they complete
}

Deadlines and cancellation:

import { deadline } from "@std/async/deadline";

await deadline(fetch("/slow"), 1_000); // throws DOMException("TimeoutError") after 1s