async-await-utils

Asynchronous I/O has a tendency to suffer a variety of contraints and/or unpredictable failures. This module provides a set of utility functions that are designed to provide optimizations, controls, fallbacks and safeguards for such scenarios.

Quick Examples:

  import { resilient, timed, throttled } from 'async-await-utils/hof';

  const randomlyFailing = () => new Promise((resolve, reject) => Math.random() > 0.5 ? reject() : resolve());
  const randomDuration = () => new Promise(resolve => setTimeout(resolve, Math.random() * 2000));
  const fastFunction = () => new Promise(resolve => setTimeout(resolve, 100));

  const failsLess = resilient(randomlyFailing, { attempts: 5 });
  const timeLimited = timed(randomDuration), { timeout: 1000 });
  const slowedDown = throttled(fastFunction, { batchSize: 2 });

  failsLess(); // resultant promise is significantly less likely to fail, since it retries 5 times
  timeLimited(); // this promise will fail if it takes longer than 1 second to execute
  Promise.all([slowedDown(), slowedDown(), slowedDown(), slowedDown()]); // instead of 100ms, this will take 200ms (batches of 2 promises max at a time)

API

Higher Order Functions

Usage: Either import { hof } from 'async-await-utils' then hof.<fn> OR import { <fn> } from 'async-await-utils/hof'

⚠️ DO NOT APPLY ANY OF THE APIS TO A PROMISE DIRECTLY. APPLY THEM A PROMISE-GENERATING FUNCTION.

Higher Order Functions take an existing (async, promise returning) function, and returns a new function with adjusted characteristics. For example, given some async function fetch that makes an API call, resilient(fetch) will return a new function that tries 3 times (in the event any attempt fails) before giving up and throwing the original error(s).

Summary:

• guarded - adds failure interception with console logging of errors
• resilient - makes retry attempts
• reuseInFlight - debounce repeat calls to an in-flight Promise
• throttled - limit parallel execution of Promises
• timed - time limit promises

Misc:

• resilientTimed - convenience composition of resilient and timed.

guarded

Guards the given asynchronous function with a try-catch, and logs out the error fully before re-throwing the error

  const failingFunction = () => throw new Error('fails');
  const guardedFunction = hof.guarded(failingFunction, <options>);

  guardedFunction(); // will log the error out

options is an optional object that can contain the following parameters:

• context - default null, binds the given function against the context before executing it.

resilient

Makes a function retry a given number of times (default 3) before giving up and re-throwing the failures.

  const unreliableFunction = threshold => if (Math.random() < threshold) throw new Error();
  const resilientFunction = hof.resilient(unreliableFunction, <options>);

  resilientFunction(0.5); // Has a 6.25% chance of throwing, improved over the passed in 50%

options is an optional object that can contain the following parameters:

• attempts - default 3, the number of times to retry before giving up.
• context - default null, binds the given function against the context before executing it.
• task - default promise resolution, just a string that is attached to the Error thrown

reuseInFlight

If a promise generating function is called with ...args, and subsequently called again with the same ...args while the first Promise is still unresolved, then the first Promise is returned instead of creating a new Promise, effectively "debouncing" the promise.

	const debounced = hof.reuseInFlight(asyncFn, <options>);

This is particularly useful for API calls that you expect to return data that is unlikely to change frequently.

The default method used to determine if ...args are the same is via JSON stringification, but this can be changed.

// assume sleep(ms) works like described in the "simple" API below
let callCount = 0;
const oneSecondFunction = () => new Promise(resolve =>
	setTimeout(() => resolve(callCount++), 1000);
);

const debounced = hof.reuseInFlight(oneSecondFunction);
const result1 = debounced(); // will return 0;
const result2 = sleep(100).then(() => debounced()) // will return 0
const result3 = sleep(1100).then(() => debounced()) // will return 1
const result3 = sleep(1100).then(() => debounced('1')) // will return 2, different args

options is an optional object that can contain the following parameters:

• createKey(args) - defaults to { return JSON.stringify(args); }, use this to customize how unique function calls are recognized
• ignoreSingleUndefined - defaults to false. In the calls above, doing sleep(100).then(debounced) is considered different from sleep(100).then(() => debounced()), because Promise resolution defaults to a minimal single undefined result. If you want to treat a single undefined arg as no args, set this to true.

throttled

Limits the maximum number of times (default 100) a promise can be executed simultaneously

  const sleep = duration => new Promise(ok => setTimeout(ok, duration));
  const loggingFunction = () => new Promise(resolve => setTimeout(() => resolve() && console.log('.'), 1000);
  const throttedFunction = throttled(rapidFunction, <options>);

	// prints 100 dots every second for 10 seconds, instead of all 1000 dots after a second
  for (let i=0; i < 1000; i+= 100) {
  	throttledFunction();
  }

options is an optional object that can contain the following parameters:

• batchSize - default 100, how many promises must fully resolve before allowing more promises to proceed
• delay - default 0. If it is preferred to wait a while before starting the next batch, specify a delay in milliseconds.

timed (time-limited)

Places an upper bound as to how long a Promise can take to resolve. If the Promise takes longer than the specified duration (default 1000ms) then it automatically fails.

Special note: Do not time-limit throttled promises - throttle time-limited promises.

  const randomDuration = () => new Promise((ok, fail) => setTimeout(0, Math.random() * 2000));
  const oneSecondMax = timed(randomDuration, { timeout: 1000 });
  Array(5).fill().map(oneSecondMax)

options is an optional object that can contain the following parameters:

• task - default promise resolution, just a string that is attached to the Error thrown
• timeout - default 1000, the maximum amount of time in milliseconds that a promise is allowed to resolve
• context - default null, binds the given function against the context before executing it.

Simple Functions (simple)

Simple functions perform some task immediately rather than returning a function. In some cases, they will take a promise-generating function as input.

sleep

Pauses execution for the given duration in ms

import { sleep } from 'async-await-utils/simple';

async function() {
	await sleep(1000);
	console.log('1 second has passed');
}

execute(asyncFn, [...args])

Runs the given asynchronous function, catching and logging any errors before rethrowing. This is useful if you want to make sure an async function's errors don't get swallowed if you forget to catch.

import { execute } from 'async-await-utils/simple';

async function main(name) {
	console.log(`hello ${name}');
	throw new Error('boom');
}

execute(main, 'world'); // logs "hello world" then will log the "boom" error even if you don't catch