JavaScript today must interact with data-intensive APIs and networks. The solution is a program that can work asynchronously instead of finishing tasks in order. In modern JavaScript, instead of callbacks you'll use promises to improve your application's performance and responsiveness. JavaScript features introduced in ES2020, ES2021, and ESNext like Promise.allSettled(), Promise.any(), and top-level await help you develop small, fast, low-profile applications. With the AbortController API, cancel a pending async request before it has completed. Modern Asynchronous JavaScript gives you an arsenal of tools to build programs that always respond to user requests, recover quickly from difficult conditions, and deliver maximum performance. Applications today must work with information on remote servers, and users expect a quick response to complex interactions at all times, whether on a high-speed 5G cellular network or slow public WiFi. JavaScript provides developers with advanced tools to coordinate the asynchronous parts of their code efficiently and deliver responsive programs. Faster applications equal happier users, which is the promise of asynchronous JavaScript. With Modern Asynchronous JavaScript you'll learn techniques for managing your async code. Features like ES2021 Promise.any() allow you to safeguard your async code from external issues that are out of your control like server downtime. You'll discover secret weapons like top-level await to initialize resources, define dependency paths dynamically, and load dependencies with a fallback implementation. You'll even learn to how to set a time limit for async requests and react if they take too long to complete. Fast, reliable applications are a must in today's world, where users demand increasingly greater amounts of data on mobile devices. Asynchronous programming may require more cautious planning than synchronous programming but the outcome is rewarding. Asynchronous JavaScript allows you to write code that is nimble but reliable, leading to programs that load faster, respond quicker, and most importantly that you can trust to function properly. What You Need: You'll need an intermediate level of JavaScript programming skills and a browser that supports features from ES2020, ES2021, and ESNext.

With the advent of HTML5, front-end MVC, and Node.js, JavaScript is ubiquitous--and still messy. This book will give you a solid foundation for managing async tasks without losing your sanity in a tangle of callbacks. It's a fast-paced guide to the most essential techniques for dealing with async behavior, including PubSub, evented models, and Promises. With these tricks up your sleeve, you'll be better prepared to manage the complexity of large web apps and deliver responsive code. With Async JavaScript, you'll develop a deeper understanding of the JavaScript language. You'll start with a ground-up primer on the JavaScript event model--key to avoiding many of the most common mistakes JavaScripters make. From there you'll see tools and design patterns for turning that conceptual understanding into practical code. The concepts in the book are illustrated with runnable examples drawn from both the browser and the Node.js server framework, incorporating complementary libraries including jQuery, Backbone.js, and Async.js. You'll learn how to create dynamic web pages and highly concurrent servers by mastering the art of distributing events to where they need to be handled, rather than nesting callbacks within callbacks within callbacks. Async JavaScript will get you up and running with real web development quickly. By the time you've finished the Promises chapter, you'll be parallelizing Ajax requests or running animations in sequence. By the end of the book, you'll even know how to leverage Web Workers and AMD for JavaScript applications with cutting-edge performance. Most importantly, you'll have the knowledge you need to write async code with confidence. What You Need: Basic knowledge of JavaScript is recommended. If you feel that you're not up to speed, see the "Resources for Learning JavaScript" section in the preface.

Completely revised and updated, this best-selling introduction to programming in JavaScript focuses on writing real applications. JavaScript lies at the heart of almost every modern web application, from social apps like Twitter to browser-based game frameworks like Phaser and Babylon. Though simple for beginners to pick up and play with, JavaScript is a flexible, complex language that you can use to build full-scale applications. This much anticipated and thoroughly revised third edition of Eloquent JavaScript dives deep into the JavaScript language to show you how to write beautiful, effective code. It has been updated to reflect the current state of Java¬Script and web browsers and includes brand-new material on features like class notation, arrow functions, iterators, async functions, template strings, and block scope. A host of new exercises have also been added to test your skills and keep you on track. As with previous editions, Haverbeke continues to teach through extensive examples and immerses you in code from the start, while exercises and full-chapter projects give you hands-on experience with writing your own programs. You start by learning the basic structure of the JavaScript language as well as control structures, functions, and data structures to help you write basic programs. Then you'll learn about error handling and bug fixing, modularity, and asynchronous programming before moving on to web browsers and how JavaScript is used to program them. As you build projects such as an artificial life simulation, a simple programming language, and a paint program, you'll learn how to: - Understand the essential elements of programming, including syntax, control, and data - Organize and clarify your code with object-oriented and functional programming techniques - Script the browser and make basic web applications - Use the DOM effectively to interact with browsers - Harness Node.js to build servers and utilities Isn't it time you became fluent in the language of the Web? * All source code is available online in an inter¬active sandbox, where you can edit the code, run it, and see its output instantly.

Asynchronous JavaScript is everywhere, whether you’re using Ajax, AngularJS, Node.js, or WebRTC. This practical guide shows intermediate to advanced JavaScript developers how Promises can help you manage asynchronous code effectively—including the inevitable flood of callbacks as your codebase grows. You’ll learn the inner workings of Promises and ways to avoid difficulties and missteps when using them. The ability to asynchronously fetch data and load scripts in the browser broadens the capabilities of JavaScript applications. But if you don’t understand how the async part works, you’ll wind up with unpredictable code that’s difficult to maintain. This book is ideal whether you’re new to Promises or want to expand your knowledge of this technology. Understand how async JavaScript works by delving into callbacks, the event loop, and threading Learn how Promises organize callbacks into discrete steps that are easier to read and maintain Examine scenarios you’ll encounter and techniques you can use when writing real-world applications Use features in the Bluebird library and jQuery to work with Promises Learn how the Promise API handles asynchronous errors Explore ECMAScript 6 language features that simplify Promise-related code

No matter how much experience you have with JavaScript, odds are you don’t fully understand the language. As part of the "You Don’t Know JS" series, this concise yet in-depth guide focuses on new asynchronous features and performance techniques—including Promises, generators, and Web Workers—that let you create sophisticated single-page web applications and escape callback hell in the process. Like other books in this series, You Don’t Know JS: Async & Performance dives into trickier parts of the language that many JavaScript programmers simply avoid. Armed with this knowledge, you can become a true JavaScript master. With this book you will: Explore old and new JavaScript methods for handling asynchronous programming Understand how callbacks let third parties control your program’s execution Address the "inversion of control" issue with JavaScript Promises Use generators to express async flow in a sequential, synchronous-looking fashion Tackle program-level performance with Web Workers, SIMD, and asm.js Learn valuable resources and techniques for benchmarking and tuning your expressions and statements

This book focuses on the new asynchronous features in JavaScript, which are new and confusing to developers. The book covers promises, generators, and coroutines, all of which allow developers to created more sophisticated single-page web applications that provide the features of a desktop application without tying up the user's browser.

Asynchronous programming is essential to the modern web and at last JavaScript programmers have the tools to do the job - the Promise object and the async and await commands. These are so elegant in their design that you need to know about them if only to be impressed. It is likely that other languages will incorporate similar facilities in the future. While async and await make asynchronous code as easy to use as synchronous code there are a lot of subtle things going on and to really master the situation you need to know about Promises and you need to know how the JavaScript dispatch queue works. Written for experienced JavaScript developers who want to get to grips with the complexities of the language, JavaScript Async guides you through the story of async. It starts with Events, which is where asynchronous programming originates, but it quickly becomes apparent that you need additional ways of dealing with long running tasks. The most basic solution is the callback and this is where async programming starts to become difficult. JavaScript used to be a single-threaded language, but with the introduction of the Web Worker you can write multi-threaded programs. Promises are the pinnacle of async programming in JavaScript and putting them together with the dispatch queue provides further advances. The way that async and await work with Promises is nothing short of amazing. The book concludes with a look at how async and await integrate with some of the latest JavaScript APIs that are based on the Promise object. The Service Worker is possibly the biggest change in the way JavaScript can be used to create programs that are just as happy being offline as online. Working with async can be confusing and disorienting, but by combining code examples and lucid explanations Ian Elliot presents a coherent explanation. If you want to work with async read this book first.