esnext-async

Patterns for asynchronous iteration in ES.next

Installing

esnext-async is available as an npm package.

Usage

Entry Points

Run

import {run} from 'esnext-async';

run(async () => {
  const foo = await fs.readFile('foo');
  await fs.writeFile('bar', foo);
});

Execute an async function, re-throwing any exceptions and making them fatal.

Loop

import {loop} from 'esnext-async';

loop(async () => {
  const value = await observable;
  console.log(value);
});

Execute an async function over and over, re-throwing any exceptions and making them fatal. loop waits until an "iteration" is complete before executing the next iteration.

TryCatch

import {tryCatch} from 'esnext-async';

app.get('/', tryCatch(async (request, response) => {
  const data = await database.read();
  res.send(data);
}));

Wrap an async callback function and re-throw any exceptions. tryCatch is useful when passing async callback functions to libraries that are unaware of async functions.

Control Flow

Parallel

import {parallel} from 'esnext-async';

test(async (t) => {
  await parallel(
    async () => {
      await browser.open('https://google.com');
    },
    async () => {
      t.is(await browser.requestLogs, 'https://google.com');
      t.is(await browser.requestLogs, 'https://google.com/some-image.png');
    }
  )
});

Start multiple sequences of async work at the same time and wait until every sequence is complete. parallel is useful for interleaving fast async calls with slow async calls. In the above example, the two assertions are executed after browser.open begins but before it resolves.

Sleep

import {sleep, run} from 'esnext-async';
run(async () => {
  await sleep();
  await sleep(1000);
});

Pauses execution using setTimeout. When given no arguments, 0 is passed to setTimeout.

Observables

Observable

import {Observable} from 'esnext-async';

const observable = new Observable((observer) => {
  setTimeout(() => {
    observer.next(1);
    setTimeout(() => {
      observer.next(2);
    }, 0);
  }, 0);
});

observable.forEach((value) => {
  console.log(value);
});

An implementation of the es-observable specification.

AwaitableObservable

import {AwaitableObservable} from 'esnext-async';

const observable = new AwaitableObservable((observer) => {
  setTimeout(() => {
    observer.next(1);
    setTimeout(() => {
      observer.next(2);
    }, 0);
  }, 0);
});

const value1 = await observable;
const value2 = await observable;

An observable that behaves like a promise that can be resolved multiple times. The AwaitableObservable provides more control over when to process values by eliminating callbacks.

Development

Getting Started

The application requires the following external dependencies:

• Node.js

The rest of the dependencies are handled through:

npm install

Run tests with:

npm test