The 'when' npm package is a robust library for working with asynchronous programming in JavaScript, particularly using promises. It provides utilities for creating, managing, and composing promises, making it easier to handle asynchronous operations and their potential complexities.
Creating Promises
This feature allows the creation of new promises. The code sample demonstrates how to create a simple promise that resolves with 'Hello, World!' after 1 second.
const when = require('when');
const promise = when.promise(function(resolve, reject) {
setTimeout(() => resolve('Hello, World!'), 1000);
});
promise.then(response => console.log(response));Chaining Promises
This feature demonstrates chaining multiple promises. It shows how to perform a series of tasks sequentially, where each task starts only after the previous one has completed.
const when = require('when');
const cleanRoom = () => when.promise(resolve => resolve('Room cleaned'));
const removeTrash = () => when.promise(resolve => resolve('Trash removed'));
const winIcecream = () => when.promise(resolve => resolve('Won ice cream'));
cleanRoom()
.then(result => {
console.log(result);
return removeTrash();
})
.then(result => {
console.log(result);
return winIcecream();
})
.then(result => console.log(result));Handling Errors
This feature involves error handling in promises. The code sample shows how to catch and handle errors that occur during the execution of promises.
const when = require('when');
const failTask = () => when.promise((resolve, reject) => reject('Failed task'));
failTask()
.then(result => console.log('Success:', result))
.catch(error => console.log('Error:', error));Bluebird is a full-featured promise library with a focus on innovative features and performance. It is similar to 'when' but often cited for its superior performance and additional features like cancellation, progress tracking, and more detailed stack traces.
Q is one of the earliest promise libraries that influenced many others. It offers a similar API to 'when' but is generally considered to be less performant in modern applications. It provides a straightforward approach to handling asynchronous operations with promises.
The 'promise' package provides a minimalist implementation similar to the ES6 Promise specification. It is more lightweight compared to 'when' but lacks some of the more advanced features and utilities provided by 'when'.
When.js is cujojs's lightweight CommonJS Promises/A and when() implementation, derived from the async core of wire.js, cujojs's IOC Container. It also provides several other useful Promise-related concepts, such as joining multiple promises, mapping and reducing collections of promises, timed promises, and has a robust unit test suite.
It passes the Promises/A Test Suite, is frighteningly fast, and is around 1.4k when compiled with Google Closure (w/advanced optimizations) and gzipped, and has no external dependencies.
deferred.progress and deferred.resolver.progress. Use deferred.notify and deferred.resolver.notify instead.when.chain. Use resolver.resolve(promise) or resolver.resolve(promise.yield) (see promise.yield) instead.when/timed module. Use when/delay and when/timeout modules instead.deferred.then.deferred.then is deprecated and will be removed in an upcoming release. Use deferred.promise.then instead.git clone https://github.com/cujojs/when or git submodule add https://github.com/cujojs/when
Configure your loader with a package:
packages: [
{ name: 'when', location: 'path/to/when/', main: 'when' },
// ... other packages ...
]
define(['when', ...], function(when, ...) { ... }); or require(['when', ...], function(when, ...) { ... });
git clone https://github.com/cujojs/when or git submodule add https://github.com/cujojs/when<script src="path/to/when/when.js"></script>when will be available as window.whennpm install whenvar when = require('when');ringo-admin install cujojs/whenvar when = require('when');Note that when.js includes @domenic's Promises/A Test Suite. Running unit tests in Node will run both when.js's own test suite, and the Promises/A Test Suite.
npm installnpm testnpm installnpm start - starts buster server & prints a urllocalhost:1111/capturenpm run-script test-browserMuch of this code was inspired by @unscriptable's tiny promises, the async innards of wire.js, and some gists here, here, here, and here
Some of the code has been influenced by the great work in Q, Dojo's Deferred, and uber.js.
1.8.1
deferred.progress and deferred.resolver.progress. Use deferred.notify and deferred.resolver.notify instead.when.chain. Use resolver.resolve(promise) or resolver.resolve(promise.yield) (see promise.yield) instead.when/timed module. Use when/delay and when/timeout modules instead.FAQs
A lightweight Promises/A+ and when() implementation, plus other async goodies.
The npm package when receives a total of 556,295 weekly downloads. As such, when popularity was classified as popular.
We found that when demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 1 open source maintainer collaborating on the project.
Did you know?
Socket for GitHub automatically highlights issues in each pull request and monitors the health of all your open source dependencies. Discover the contents of your packages and block harmful activity before you install or update your dependencies.
Security News
Node.js will be enforcing stricter semver-major PR policies a month before major releases to enhance stability and ensure reliable release candidates.
Security News
Research
Socket's threat research team has detected five malicious npm packages targeting Roblox developers, deploying malware to steal credentials and personal data.
Security News
vlt introduced its new package manager and a serverless registry this week, innovating in a space where npm has stagnated.