This book is designed to be a resource that provides a set of tools and techniques to successfully navigate the challenges of building large-scale, maintainable, and scalable javascript web applications using React. Many of the ideas apply more broadly. In the first half of the book, we delve into the essentials, adopting a practical, example-led strategy. We start with the basics of understanding how software complexity can be managed before addressing key concepts such as design systems, data fetching, and state management, ensuring you understand how to structure and scale your React applications effectively. After closing the first part, we explore other topics like translation and internationalization (i18n), and how code folders and files can be neatly organized. In the second half of the book, we dive into more sophisticated areas necessary for full-scale application development. Here, we tackle the challenges of personalization, AB testing, scalable web architecture, and caching strategies. You’ll learn how to approach technical migrations, ensuring that your application remains cutting-edge and maintainable. Finally, we conclude by discussing the advantages TypeScript provides in making React code “safe” and the importance of testing.