delay

What is delay?

The 'delay' npm package is a simple utility that allows you to pause the execution of an asynchronous function for a specified amount of time. It is primarily used to introduce delays in promise chains or async functions, making it useful for testing, rate limiting, or creating time-based behavior in applications.

What are delay's main functionalities?

Basic Delay

This feature allows you to pause the execution of code within an async function for a specified duration (in milliseconds). In this example, the code waits for 2 seconds before printing '2 seconds later'.

const delay = require('delay');

(async () => {
  console.log('Waiting...');
  await delay(2000);
  console.log('2 seconds later');
})();

Delay with Value

This feature enables you to resolve a promise with a specific value after a delay. Here, the promise resolves with the string 'Hello after 1.5 seconds' after waiting for 1.5 seconds.

const delay = require('delay');

(async () => {
  const result = await delay(1500, {value: 'Hello after 1.5 seconds'});
  console.log(result);
})();

Delay with Options

This feature supports passing an options object that can include an AbortSignal to cancel the delay. If the abort signal is triggered, the delay is cancelled, and the subsequent code may not execute.

const delay = require('delay');

(async () => {
  await delay(1000, {signal: someAbortSignal});
  console.log('This will not run if the abort signal is triggered');
})();

Other packages similar to delay

timeout

Similar to 'delay', 'timeout' is used to introduce a delay in asynchronous operations. However, it focuses more on setting timeouts for promises, potentially rejecting them if they take too long, which is a slight functional shift from simply delaying.

sleep-promise

This package offers functionality similar to 'delay' by resolving a promise after a specified timeout. The main difference is in the API design and naming conventions, but the core functionality of introducing delays in promise-based workflows is very similar.

p-timeout

While 'p-timeout' provides delay functionalities, it is primarily designed to add timeout capabilities to promises. It can reject a promise if it does not settle within a specified period, which is a feature not provided by 'delay'.

README

delay

Delay a promise a specified amount of time

If you target Node.js 15 or later, you can do await require('timers/promises').setTimeout(1000) instead.

Install

$ npm install delay

Usage

const delay = require('delay');

(async () => {
	bar();

	await delay(100);

	// Executed 100 milliseconds later
	baz();
})();

API

delay(milliseconds, options?)

Create a promise which resolves after the specified milliseconds.

delay.reject(milliseconds, options?)

Create a promise which rejects after the specified milliseconds.

delay.range(minimum, maximum, options?)

Create a promise which resolves after a random amount of milliseconds between minimum and maximum has passed.

Useful for tests and web scraping since they can have unpredictable performance. For example, if you have a test that asserts a method should not take longer than a certain amount of time, and then run it on a CI, it could take longer. So with .range(), you could give it a threshold instead.

milliseconds

mininum

maximum

Type: number

Milliseconds to delay the promise.

options

Type: object

value

Type: unknown

Optional value to resolve or reject in the returned promise.

signal

Type: AbortSignal

The returned promise will be rejected with an AbortError if the signal is aborted. AbortSignal is available in all modern browsers and there is a ponyfill for Node.js.

delayPromise.clear()

Clears the delay and settles the promise.

delay.createWithTimers({clearTimeout, setTimeout})

Creates a new delay instance using the provided functions for clearing and setting timeouts. Useful if you're about to stub timers globally, but you still want to use delay to manage your tests.

Advanced usage

Passing a value:

const delay = require('delay');

(async() => {
	const result = await delay(100, {value: '🦄'});

	// Executed after 100 milliseconds
	console.log(result);
	//=> '🦄'
})();

Using delay.reject(), which optionally accepts a value and rejects it ms later:

const delay = require('delay');

(async () => {
	try {
		await delay.reject(100, {value: new Error('🦄')});

		console.log('This is never executed');
	} catch (error) {
		// 100 milliseconds later
		console.log(error);
		//=> [Error: 🦄]
	}
})();

You can settle the delay early by calling .clear():

const delay = require('delay');

(async () => {
	const delayedPromise = delay(1000, {value: 'Done'});

	setTimeout(() => {
		delayedPromise.clear();
	}, 500);

	// 500 milliseconds later
	console.log(await delayedPromise);
	//=> 'Done'
})();

You can abort the delay with an AbortSignal:

const delay = require('delay');

(async () => {
	const abortController = new AbortController();

	setTimeout(() => {
		abortController.abort();
	}, 500);

	try {
		await delay(1000, {signal: abortController.signal});
	} catch (error) {
		// 500 milliseconds later
		console.log(error.name)
		//=> 'AbortError'
	}
})();

Create a new instance that is unaffected by libraries such as lolex:

const delay = require('delay');

const customDelay = delay.createWithTimers({clearTimeout, setTimeout});

(async() => {
	const result = await customDelay(100, {value: '🦄'});

	// Executed after 100 milliseconds
	console.log(result);
	//=> '🦄'
})();

Related

• delay-cli - CLI for this module
• p-cancelable - Create a promise that can be canceled
• p-min-delay - Delay a promise a minimum amount of time
• p-immediate - Returns a promise resolved in the next event loop - think setImmediate()
• p-timeout - Timeout a promise after a specified amount of time
• More…