Concurrency in JavaScript (Node.js): Asynchrony, Threads, Parallelism

The book "Concurrency in JavaScript (Node.js)" is a practical guide to creating high-performance, responsive, and scalable applications on the Node.js platform. In the modern world of web development, the speed and efficiency of server-side code directly impact user experience and infrastructure costs. This book will help you master all the key concepts of concurrent programming, from the basics of asynchrony to advanced multithreading techniques.

Who this book is for:

• JavaScript developers transitioning to server-side development with Node.js;
• Backend engineers looking to deepen their knowledge of asynchronous programming;
• Developers facing performance issues and blocking in Node.js;
• Anyone who wants to understand how the Event Loop works and how to efficiently use system resources.

What you will learn from this book:

• How the Event Loop in Node.js is structured and its phases (timers, I/O callbacks, idle, poll, check, close);
• The difference between synchronous, asynchronous, and concurrent code execution;
• An in-depth understanding of Promises, then/catch chains, and static methods (Promise.all, Promise.race, Promise.allSettled);
• Proper use of async/await for writing readable asynchronous code;
• Error handling in asynchronous functions and promises;
• Working with Streams for processing large volumes of data;
• Multithreading with Worker Threads: creating workers, data transfer, shared memory (SharedArrayBuffer);
• Clustering Node.js applications to maximize CPU core utilization;
• Design patterns for concurrent applications: Producer-Consumer, Pub/Sub, Pipeline;
• Profiling and debugging asynchronous code, finding memory leaks and blockages;
• Safety in multithreaded applications: avoiding race conditions and deadlocks.

The book is structured on the principle of "from simple to complex": each chapter contains a theoretical foundation, clear code examples, and practical tasks for reinforcing the material. You will learn not only to write asynchronous code but also to understand how Node.js manages tasks under the hood.

Special attention is given to comparing concurrency in Node.js with other approaches (multithreading in C++/Java, asynchrony in Python asyncio). This will help you see the big picture and choose the right tools for each task.

After reading the book, you will be able to create high-load web servers, chat applications, file processors, and any other systems that require efficient use of CPU and I/O resources. You will stop fearing "callback hell" and learn to design architecture that is resistant to blocking.

The book is suitable both for beginner developers with basic knowledge of JavaScript and for experienced engineers who want to systematize their knowledge of concurrency in Node.js.