Last updated April 2025.

Welcome to the exciting world of browser extension development! This book is designed to guide you through the process of creating your own browser extensions, using technologies you might already be familiar with like JavaScript, React, and Express. Whether you're looking to enhance your browsing experience, improve productivity, or even build something entirely new, this journey will equip you with the skills needed to bring your ideas to life.

This guide is tailored for junior developers or anyone with a basic understanding of web technologies who wants to step into the world of browser extensions. We assume you have a fundamental grasp of JavaScript, as well as some familiarity with React, and Express. However, when it comes to extension-specific concepts, we'll dive into detailed explanations and step-by-step instructions to ensure you can follow along, regardless of your prior experience with browser extensions.

By the end of this book, you will have learned:

• The basics of browser extensions and how they work.
• How to set up your development environment for building extensions.
• How to create interactive and dynamic extensions using JavaScript and React.
• How to handle background processes and communications in extensions using Express.
• Best practices for debugging and testing your extensions.
• How to publish your extensions to browsers like Chrome and Firefox.

The book is structured into five comprehensive chapters:

1. Browser extension basics, Development setup
2. Setting up a Node.js server with TypeScript, Express.js, and Yarn
3. User Authentication
4. Implementing stripe subscriptions
5. Adding LLM Feature and Deployment

Each chapter is crafted to build upon the knowledge gained in the previous ones, progressively enhancing your skills and understanding of browser extension development.

Take a look at the final code and the codebase for each chapter.

We built:

• and maintain two popular repos (combined: over 8000 stars and 1000 unique visitors per week).
• and maintain the most popular React/TypeScript/Node boilerplate for starting a SaaS business.
• LoadFlow, growing niche job board for biotech startups.
• Work in biotech, popular job board for biotech startups.
• Harbor, all-in-one platform for recruiting agencies and independent recruiters.
• dozen+ SaaS web applications in the last 15 years.

You can find us on GitHub:

• Kelly: GitHub, LinkedIn
• Tim: GitHub, LinkedIn

Last updated April 2025.