p-defer

What is p-defer?

The p-defer package is a utility for creating deferred promises in JavaScript. It allows you to create a promise and expose its resolve and reject functions, which can be called later to settle the promise. This is useful for scenarios where you need to control the timing of when a promise is resolved or rejected.

What are p-defer's main functionalities?

Creating a Deferred Promise

This feature allows you to create a deferred promise and resolve it at a later time. The `pDefer` function returns an object with a `promise` property and `resolve` and `reject` methods. You can use the `promise` property to await the promise and call `resolve` or `reject` to settle it.

const pDefer = require('p-defer');

const deferred = pDefer();

// Use the promise
async function example() {
  await deferred.promise;
  console.log('Promise resolved!');
}

example();

// Resolve the promise later
setTimeout(() => {
  deferred.resolve();
}, 1000);

Handling Errors with Deferred Promises

This feature demonstrates how to handle errors with deferred promises. You can call the `reject` method to reject the promise with an error, and handle the error using a try-catch block when awaiting the promise.

const pDefer = require('p-defer');

const deferred = pDefer();

// Use the promise
async function example() {
  try {
    await deferred.promise;
  } catch (error) {
    console.error('Promise rejected:', error);
  }
}

example();

// Reject the promise later
setTimeout(() => {
  deferred.reject(new Error('Something went wrong'));
}, 1000);

Other packages similar to p-defer

deferred

The 'deferred' package provides similar functionality to p-defer by allowing you to create deferred promises. It also exposes the resolve and reject methods, but it includes additional features like progress notifications and chaining. It is more feature-rich compared to p-defer.

promise-defer

The 'promise-defer' package is another alternative that provides deferred promises. It is lightweight and straightforward, similar to p-defer, but it does not include any additional features beyond basic deferred promise functionality.

bluebird

The 'bluebird' package is a fully-featured promise library that includes deferred promises among many other advanced features like cancellation, progress, and concurrency control. It is more comprehensive and powerful compared to p-defer, but also more complex.

README

p-defer

Create a deferred promise

Don't use this unless you know what you're doing. Prefer the Promise constructor.

Install

npm install p-defer

Usage

import pDefer from 'p-defer';

function delay(milliseconds) {
	const deferred = pDefer();
	setTimeout(deferred.resolve, milliseconds, '🦄');
	return deferred.promise;
}

console.log(await delay(100));
//=> '🦄'

The above is just an example. Use delay if you need to delay a promise.

API

pDefer()

Returns an object with a promise property and functions to resolve() and reject().

Related

• p-lazy - Create a lazy promise that defers execution until .then() or .catch() is called
• More…