Book Image

JavaScript Concurrency

By : Adam Boduch
Book Image

JavaScript Concurrency

By: Adam Boduch

Overview of this book

Concurrent programming may sound abstract and complex, but it helps to deliver a better user experience. With single threaded JavaScript, applications lack dynamism. This means that when JavaScript code is running, nothing else can happen. The DOM can’t update, which means the UI freezes. In a world where users expect speed and responsiveness – in all senses of the word – this is something no developer can afford. Fortunately, JavaScript has evolved to adopt concurrent capabilities – one of the reasons why it is still at the forefront of modern web development. This book helps you dive into concurrent JavaScript, and demonstrates how to apply its core principles and key techniques and tools to a range of complex development challenges. Built around the three core principles of concurrency – parallelism, synchronization, and conservation – you’ll learn everything you need to unlock a more efficient and dynamic JavaScript, to lay the foundations of even better user experiences. Throughout the book you’ll learn how to put these principles into action by using a range of development approaches. Covering everything from JavaScript promises, web workers, generators and functional programming techniques, everything you learn will have a real impact on the performance of your applications. You’ll also learn how to move between client and server, for a more frictionless and fully realized approach to development. With further guidance on concurrent programming with Node.js, JavaScript Concurrency is committed to making you a better web developer. The best developers know that great design is about more than the UI – with concurrency, you can be confident every your project will be expertly designed to guarantee its dynamism and power.
Table of Contents (17 chapters)
JavaScript Concurrency
About the Author
About the Reviewer


This chapter covered a lot of details about the Promise object introduced in ES6 to help JavaScript programmers deal with synchronization issues that have plagued the language for years. With asynchronicity comes callbacks—lots of callbacks. This creates a callback hell that we want to avoid at all costs.

Promises help us deal with synchronization issues by implementing a simple interface that's generic enough to resolve any value. Promises are always in one of three states—pending, fulfilled, or rejected, and they only change their state once. When these state changes happen, callbacks are triggered. Promises have an executor function, whose job is to set up the asynchronous actions that use a promise resolver or rejector function to change the state of the promise.

Much of the value that promises bring to the table is about how they help us simplify complex scenarios. Because, if we only had to deal with a single asynchronous action that runs a callback with a resolved value, promises...