std/async

async

async is a module to provide help with asynchronous tasks.

Usage

The following functions and class are exposed in mod.ts:

deferred

Create a Promise with the reject and resolve functions.

import { deferred } from "https://deno.land/std/async/mod.ts";

const p = deferred<number>();
// ...
p.resolve(42);

delay

Resolve a Promise after a given amount of milliseconds.

import { delay } from "https://deno.land/std/async/mod.ts";

// ...
const delayedPromise = delay(100);
const result = await delayedPromise;
// ...

MuxAsyncIterator

The MuxAsyncIterator class multiplexes multiple async iterators into a single stream.

The class makes an assumption that the final result (the value returned and not yielded from the iterator) does not matter. If there is any result, it is discarded.

import { MuxAsyncIterator } from "https://deno.land/std/async/mod.ts";

async function* gen123(): AsyncIterableIterator<number> {
  yield 1;
  yield 2;
  yield 3;
}

async function* gen456(): AsyncIterableIterator<number> {
  yield 4;
  yield 5;
  yield 6;
}

const mux = new MuxAsyncIterator<number>();
mux.add(gen123());
mux.add(gen456());
for await (const value of mux) {
  // ...
}
// ..

pooledMap

Transform values from an (async) iterable into another async iterable. The transforms are done concurrently, with a max concurrency defined by the poolLimit.

import { pooledMap } from "https://deno.land/std/async/mod.ts";

const results = pooledMap(
  2,
  [1, 2, 3],
  (i) => new Promise((r) => setTimeout(() => r(i), 1000)),
);

for await (const value of results) {
  // ...
}

tee

Branches the given async iterable into the n branches.

import { tee } from "https://deno.land/std/async/tee.ts";

const gen = async function* gen() {
  yield 1;
  yield 2;
  yield 3;
};

const [branch1, branch2] = tee(gen());

(async () => {
  for await (const n of branch1) {
    console.log(n); // => 1, 2, 3
  }
})();

(async () => {
  for await (const n of branch2) {
    console.log(n); // => 1, 2, 3
  }
})();