Understanding JavaScript Promises
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Understanding JavaScript Promises

About the Book

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 is written to introduce the promises and their intricacies in a straightforward, easy to read format. Each chapter is filled with practical, real-world examples using the techniques discussed, and all examples are available for download with your purchase.

What you'll learn:

  • Which parts of promises are synchronous and which are asynchronous
  • How to effectively use promise chains to simplify your code
  • The best way to catch errors in promises
  • How to create your own promises
  • Ways to work with multiple promises at once
  • How async functions and await expression hide promise complexities
  • How to abort asynchronous functions and create your own abortable functions
  • What happens to rejected promises without rejection handlers

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About the Author

Nicholas C. Zakas
Nicholas C. Zakas

Nicholas C. Zakas is an independent software engineer, consultant, coach, and has authored over a dozen books. He created the ESLint open source project and has worked on everything from small websites to massive-scale web applications. He has worked at Box as a principal architect and Yahoo as a presentation architect. Nicholas is a strong advocate for development best practices including progressive enhancement, accessibility, performance, scalability, and maintainability.

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. Abortable Functions
    • Using an AbortController Object
    • Custom Signals with AbortSignal
    • Creating Abortable Functions
    • Summary
  • 6. Unhandled Rejection Tracking
    • Detecting Unhandled Rejections
    • Web Browser Unhandled Rejection Tracking
    • Node.js Unhandled Rejection Tracking
    • Summary
  • Final Thoughts
    • Download the Extras
    • Help and Support
    • Follow the Author
  • Notes

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