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

Resolving and rejecting promises

If the preceding section just introduced several new terms that sounded confusing, then don't worry. We'll see what all these promise terms look like in practice, starting with this section. Here, we'll perform some straightforward promise resolving and rejecting.

Resolving promises

The resolver is a function that, as the name implies, resolves a promise for us. It's not the only way to resolve a promise—we'll explore more advanced techniques later on in the chapter. But this method is, by far, the most common. It's passed into the executor function as the first argument. This means that the executor can resolve the promise directly by simply calling the resolver. But this wouldn't provide us with much utility, would it?

The common case to a greater extent is for the promise executor function to set up the asynchronous actions that are about to take place—things such as making network calls. Then, in the callback functions for these asynchronous actions, we...