Understanding JavaScript Promises

Since promises were added to JavaScript in 2015, they have become an integral part of the language. A good understanding of how promises work is more important than ever in becoming a proficient JavaScript developer. This book begins by explaining the basic concepts behind promises, including what they are, how to use them, and how to create your own. You'll then build upon these basic concepts to learn how to chain promises together and how to respond to multiple promises at once. Once you've learned these advanced concepts, you'll move on to learn how promises work with async functions and how to track unhandled promise rejections. All of the concepts discussed are grounded in real world examples so you learn not just how to use a particular technique, but also why and when to use it. It doesn't matter if you're writing JavaScript for web browsers, Node.js, or Deno, this book will teach you everything you need to know about promises. Table of Contents Introduction About This Book Acknowledgments About the Author Disclaimer 1. Promise Basics The Promise Lifecycle Creating New (Unsettled) Promises Creating Settled Promises Summary 2. Chaining Promises Catching Errors Using finally() in Promise Chains Returning Values in Promise Chains Returning Promises in Promise Chains Summary 3. Working with Multiple Promises The Promise.all() Method The Promise.allSettled() Method The Promise.any() Method The Promise.race() Method Summary 4. Async Functions and Await Expressions Defining Async Functions What Makes Async Functions Different Summary 5. Unhandled Rejection Tracking Detecting Unhandled Rejections Web Browser Unhandled Rejection Tracking Node.js Unhandled Rejection Tracking Summary Final Thoughts Download the Extras Support the Author Help and Support Follow the Author