Facebook is one of the biggest tech companies in the world, with over 2.8 billion monthly active users as of the third quarter of 2022. As a leading social media platform, Facebook relies heavily on web and mobile applications to power its products and services.
React is a JavaScript library developed and open-sourced by Facebook in 2013. Since then, React has become one of the most popular front-end frameworks used by web developers around the world. But how exactly does Facebook itself use React and what benefits does it provide?
The History of React at Facebook
The origins of React go back to 2011 when Facebook engineers Jordan Walke and Pete Hunt were working on Facebook’s News Feed feature. At the time, the challenge was optimizing News Feed to display updates in real-time while handling the large amount of traffic Facebook received.
To solve this problem, Walke created a new JavaScript library called FaxJS that implemented a virtual DOM – a fast and lightweight in-memory representation of the actual DOM. This allowed the team to minimize expensive DOM operations and re-render only components that needed updating, thus improving overall performance.
In 2012, the FaxJS library was adapted and reused to build Facebook’s first native mobile app. Eventually, it was decided to open source FaxJS under a new name – React.
React was first deployed on Facebook’s News Feed in early 2013 and immediately proved impactful. News Feed went from taking 300ms+ to render update to finishing in less than 50ms. The improvement in latency and responsiveness was a game-changer.
Over the following years, React adoption steadily grew within Facebook. It became the standard front-end library for new web projects and was ported to other platforms like React Native for mobile development.
Why Facebook Chose React
There are several key reasons why React emerged as the front-end framework of choice at Facebook:
- Performance: React implements a virtual DOM and intelligently minimizes DOM operations for faster UI rendering and updates. This boosts overall app performance, especially on larger, data-heavy apps like Facebook.
- Modularity: React components are encapsulated and reusable, making it easy to build complex UIs from simple building blocks. This modularity enables greater code organization and simplifies development.
- Flexibility: React can be used across different platforms (web, mobile, VR) thanks to framework portability. This flexibility allowed Facebook to standardize on one front-end library.
- Testability: The component model of React promotes writing code that is highly testable. This complements Facebook’s extensive testing culture and need for reliability at scale.
- Developer experience: React provides a smooth developer experience with modern ES6+ JavaScript syntax, extensive documentation, and a large open-source ecosystem of tools and libraries.
Together, these technical advantages and developmental benefits made React a logical choice as Facebook’s front-end JavaScript framework.
Where is React Used at Facebook?
As a core front-end technology, React is widely used across Facebook’s web and mobile apps. Some of the most significant uses and implementations include:
News Feed
As mentioned earlier, News Feed was the original problem space that inspired React. Today, React remains essential to rendering the endless feed of posts, videos, ads, and more that users scroll through.
On the News Feed specifically, React enables efficient re-rendering of the rapidly changing post content. As users scroll, React only updates the feed components visible on screen rather than having to re-render everything.
Ads Manager
Facebook Ads Manager is the platform used by businesses to manage their advertising campaigns on Facebook, Instagram, and other services. This complex interface relies on React to deliver a smooth experience.
React allows the Ads Manager to handle numerous dynamic components and data while providing seamless navigation and interactions. Features like live campaign reporting particularly benefit from React’s performance optimizations.
Business Manager
Similar to Ads Manager, Business Manager is another major management interface built with React. It enables businesses to manage their presence across Facebook’s suite of apps and services.
React empowers recursive UI rendering within Business Manager, such as nested menus and hierarchical account structures. Smooth navigation and transitions between sections provide a polished user experience.
Messenger Web and Mobile Apps
The Messenger apps for both web and mobile use React to construct the messaging interface and threads. React React handles challenges like optimistic updates and smooth scrolling for long chat histories.
Additionally, features like message reactions are powered by React components. The simple act of adding an emoji reaction relies on many React processes running under the hood.
Instagram Web Experience
Instagram’s mobile apps are built with React Native, while the Instagram website relies on React to deliver a top-notch browsing experience.
React enables seamless transitions between Instagram’s content feed, stories, reels, and more. Complex functionality like commenting, messaging, and creating posts are also made possible by React’s capabilities.
Virtual Reality Apps
Facebook utilizes React VR and React 360 to build immersive virtual reality experiences. Apps like Facebook Spaces leverage these React-based frameworks.
The declarative nature of React is well-suited for constructing VR environments. React integration with VR platforms allows Facebook to reuse web development skills for cutting-edge applications.
React Architecture at Facebook
At a high-level, this is how React is architected within Facebook’s web codebase:
- The front-end is built using React components, which generate the HTML views rendered on the client-side.
- For the back-end, Facebook uses a PHP-based API server to handle data fetching, processing, and business logic.
- React communicates with the back-end via API calls made using Facebook’s Relay framework.
- The React components fetch data by sending GraphQL queries through Relay, which interfaces with the PHP API.
- Flux architecture patterns help manage data flow and app state within React.
- Facebook uses Jest for testing its React components and apps.
This stack combining React, Relay, GraphQL, and other tools allows Facebook to build complex web experiences that can handle its massive scale.
React Performance Optimizations
With React being such a critical part of its web and mobile apps, Facebook employs extensive performance optimizations and best practices:
Virtualization
Virtualizing resource-heavy components allows Facebook to minimize DOM size and reduce rendering operations. Virtual windows track off-screen content.
Windowing
Windowing the viewport to only render visible components improves scrolling and resizing performance. As users scroll, window sizes shift dynamically.
Async Rendering
Using async rendering allows components to finish work separately from the main thread. This improves perceived performance and responsiveness.
Server-Side Rendering
For initial page loads, server-side rendering in React provides a big boost by sending fully rendered HTML from the backend.
Pre-Fetching
Data and component code for links that users are likely to click can be pre-fetched. This makes navigation faster when users actually click.
Code Splitting
Code splitting and dynamic loading allows apps to only load code required for the initial route. Other routes can load lazily as needed.
CSS in JS
Using CSS-in-JS techniques like Styled Components eliminates extra network requests. Styles are combined with components for efficient loading.
Testing React at Facebook
To ensure code quality for its React apps and components, Facebook deeply embraces testing:
- Unit testing individual components with Jest provides a safety net for interface code.
- Snapshot testing catches unexpected UI regressions during new development.
- End-to-end testing with frameworks like Selenium continuously validates flows and functionality.
- Shallow rendering optimizes test speed by minimizing rendered trees.
- Static analysis with Flow and ESLint maintains code hygiene and style consistency.
Extensive use of testing methodologies helps Facebook ship React apps with confidence. Automated testing also aids long-term maintainability and developer productivity.
React Community at Facebook
Facebook and its engineering teams actively participate in and give back to the broader React community:
- Open source – Facebook has open sourced nearly all key React libraries, tools, and extensions.
- Documentation – The official React docs provide in-depth learning resources to the community.
- Conferences – Facebook engineers speak frequently at React conferences worldwide.
- Online forums – Engineers participate in forums like GitHub issues and Stack Overflow to answer questions.
- Blog posts – Technical articles detail React optimizations and new capabilities at Facebook.
- Podcasts – The “React Podcast” featured Facebook engineers discussing React news.
By being involved with React’s open source community, Facebook helps nurture the next generation of web developers and ensures React’s continued growth and adoption.
The Future of React at Facebook
React has become an indispensable part of web development at Facebook. After a decade of continuous improvement and optimization, the framework is better positioned than ever for the future.
Facebook continues investing in React’s evolution:
- Staying on the cutting edge with frameworks like React Native and ReasonML.
- Exploring future web capabilities like React Server Components.
- Improving developer productivity with tools like GraphQL and Prepack.
- Driving performance breakthroughs with techniques like async rendering.
Given React’s central role at Facebook, the framework will undoubtedly continue to grow in usage and capabilities for many years to come.
Conclusion
React’s journey at Facebook over the past decade exemplifies how the right technology choice can meet evolving business needs. React’s emphasis on modularity, performance, and developer experience made it the ideal front-end framework as Facebook scaled its apps to serve billions of users worldwide.
Facebook’s extensive use of React across its web, mobile, and VR experiences is a testament to the framework’s versatility. The company’s massive investment into React’s performance and developer community demonstrates the long-term strategic value it brings.
Looking ahead, Facebook is sure to remain at the forefront of React innovation. Given the framework’s effectiveness thus far, React is positioned to be a critical part of Facebook’s front-end infrastructure for many years to come.