Facebook is one of the most popular social media platforms in the world, with over 2.8 billion monthly active users as of Q3 2022. With so many people using Facebook every day, it’s no surprise that the underlying technology powering the platform is complex and constantly evolving.
One common question developers and tech enthusiasts ask is whether Facebook is built with React. React is an open-source JavaScript library created by Facebook for building user interfaces. Since its release in 2013, React has become one of the most widely used front-end libraries for web application development.
So is Facebook actually built with React? The short answer is yes, Facebook uses React extensively in its web and mobile applications. However, it’s not quite as simple as saying Facebook is a “React app.” Let’s take a deeper look at how Facebook leverages React and other technologies to build its products.
Facebook’s Tech Stack
Facebook’s front-end tech stack utilizes a variety of languages, frameworks, and libraries:
- JavaScript – The core language used across Facebook’s web apps.
- React – Used for constructing reusable UI components.
- Relay – Facebook’s homegrown GraphQL client for retrieving data.
- Flow – A static type checker used to detect bugs.
- CSS/Stylus – For styling interface elements.
On the back-end, Facebook uses a mix of languages and frameworks like PHP, Python, Java, Thrift, GraphQL, and more. The back-end handles things like data storage and processing, account management, News Feed generation, ad serving, and other core platform functionality.
Now let’s dive deeper into how React fits into the puzzle.
React at Facebook
Facebook first introduced React to the world at JSConf US in May 2013. The library was born out of Facebook’s need to build complex, interactive UI components while keeping code modular and performant. Some key facts about Facebook’s use of React:
- React is used extensively in Facebook’s web apps like facebook.com, Messenger, and Instagram web.
- React is also used in Facebook’s mobile apps via React Native, which compiles to native UI components.
- Hundreds of Facebook engineers work on maintaining and improving React and related libraries like Jest and Relay.
- Facebook continues to add major new features to React, like Concurrent Mode and Suspense for Data Fetching.
Here are some examples of how Facebook leverages React:
News Feed
The Facebook News Feed is one of the most complex parts of the app, both in terms of engineering and product design. The Feed displays a personalized mix of posts, ads, and recommendations based on each user’s interests and connections. React allows Facebook’s engineers to encapsulate different parts of the News Feed like posts, comments, images, videos, and ads into modular components. These components can be reused, rearranged, and updated independently without affecting the rest of the UI.
Messenger
Facebook Messenger is built with React. Messenger has chat threads, real-time messaging, video calling, Stories, and many other interactive experiences. React’s component model allows the Messenger team to build these complex features while maintaining a fast, app-like feel. For example, chat conversations are assembled from message components rendered with React.
Instagram Web
Instagram’s mobile apps are built with React Native, but Instagram also has a website at instagram.com. The Instagram web app allows users to browse feeds, post photos, edit profiles, and more. Under the hood, the Instagram web UI is powered by React components written in JavaScript.
Facebook Gaming
Facebook Gaming lets users stream, watch, and connect around gaming content. The website and apps incorporate video playback, chat, real-time comments, and other intense interactive elements well-suited for React. Game live streams, for instance, are composed using React components.
Facebook Business Tools
Facebook equips businesses with tools to manage ads, pages, and analytics. Apps like Facebook Business Manager and Facebook Creator Studio are built with React for crafting their management interfaces and dashboards. React enables the Business Tools team to iterate quickly when building these internal-facing products.
Benefits of React for Facebook
There are several key reasons why React is a good fit for Facebook:
Modular Components
React promotes composing UIs from self-contained, reusable components. This aligns with Facebook’s product development philosophy of “Move Fast and Break Things.” Engineers can make changes to small parts of the UI without worrying about breaking larger parts.
Declarative Programming
React uses a declarative paradigm where developers describe UIs as a function of state rather than imperatively manipulating the DOM. This makes UIs more predictable and easier to debug.
Improved Performance
React uses a virtual DOM diffing algorithm to minimize costly DOM operations. This results in faster UI updates compared to traditional MVC frameworks.
Cross-Platform Code Reuse
React components written for web can be reused with React Native on Android, iOS, and other platforms, allowing code reuse across different teams at Facebook.
Active Open Source Community
React has one of the largest and most vibrant open source communities. Facebook benefits from community contributions to the core library as well as the React ecosystem.
Limitations of React for Facebook
However, React is not a silver bullet. Here are some challenges Facebook faces by using React:
Learning Curve
React introduces many new concepts like JSX, the virtual DOM, and unidirectional data flow. This can make it difficult for new engineers to onboard and work effectively.
Fragmentation
Keeping up with the fast-paced React ecosystem and version releases requires significant resources. Facebook has to deal with fragmentation across different versions.
Non-Web Platforms
React Native allows sharing code across iOS and Android, but it still requires platform-specific expertise. Games, VR, and other groups at Facebook build completely separate native apps.
Testing Challenges
React’s declarative approach can make it challenging to fully test UI logic compared to traditional imperative code.
CSS in JS Solutions
React abstracts CSS styling into JavaScript, but solutions like Styled Components add complexity for managing styles across a massive codebase.
Conclusion
In summary, Facebook extensively leverages React to build its web and mobile apps. React’s component model, declarativeness, and performance align with Facebook’s product development needs. However, using React also comes with tradeoffs that Facebook’s engineering teams must continually address.
Facebook will likely continue investing heavily in React, Relay, and related technologies for the foreseeable future. But the company will also continue innovating on new solutions that improve developer productivity and allow them to “Move Fast and Break Things” at massive scale.