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

Install

$ npm install --save delay

Usage

const delay = require('delay');

delay(200)
	.then(() => {
		// executed after 200 milliseconds
	});

somePromise()
	.then(delay(100))
	.then(result => {
		// executed 100 milliseconds after somePromise resolves
		// the result from somePromise is passed through
	});

// and with Babel and async functions
async () => {
	bar();

	await delay(100);

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

// there's also delay.reject() that takes the value, and rejects it `ms` later
Promise.resolve('foo')
	.then(delay.reject(100))
	.then(x => blah()) // never executed
	.catch(err => {
		// executed 100 milliseconds later
		// err === 'foo'
	});

// you can also specify the rejection value
Promise.resolve('foo')
	.then(delay.reject(100, 'bar'))
	.then(x => blah()) // never executed
	.catch(err => {
		// executed 100 milliseconds later
		// err === 'bar'
	});

Related

• immediate-promise - Returns a promise resolved in the next event loop - think setImmediate()

License

MIT © Sindre Sorhus