Published on 15.2.2020
React 17 is here, and while there are no huge new features or breaking changes, the update brings important improvements that make working with React smoother and more flexible than ever. In this post, we’ll dive into what’s changed in React 17, why these changes matter, and how they benefit developers, especially those working on larger applications or managing multiple versions of React.
What’s New in React 17?
React 17 is primarily a “stepping stone” release. Instead of introducing major features, the React team focused on improving the framework’s stability and enhancing the developer experience. This approach allows for easier upgrades and makes it easier to build more robust applications. Let’s look at the key updates:
1. Improved Event Handling
One of the most significant changes in React 17 is the update to event handling. React 17 introduces a new event system, which lays the foundation for future features like Concurrent Mode. Although most developers won’t notice this change directly, the new system is crucial for improving React’s performance and making it easier to integrate React with other JavaScript libraries or frameworks.
What Changed?
- Event Delegation: React has always used event delegation to manage events efficiently. In React 17, the event delegation system is reworked to use modern browser APIs, such as
EventTarget.addEventListener, instead of relying ondocument.addEventListener(which React previously used globally). - No More Global Event Listeners: Previously, React attached global event listeners to the
documentobject. This was necessary for handling events like clicks and key presses. However, it caused some issues with server-side rendering and third-party integrations. In React 17, the event listeners are now attached to the root DOM container instead, which resolves many of these problems and leads to better performance and more predictable behavior.
Why It Matters
- Better Compatibility: The new event system improves compatibility with other libraries and frameworks that also use event handling, reducing potential conflicts and making it easier to integrate React with third-party tools.
- Optimized Performance: Since React no longer uses global event listeners, performance is improved—especially in large applications where excessive event handling could lead to memory leaks or slowdowns.
- Concurrent Mode: React 17 sets the stage for enabling Concurrent Mode in the future. This mode will allow React to interrupt and pause rendering processes, improving responsiveness and interactivity. The new event system helps ensure that Concurrent Mode works seamlessly with React’s existing event-handling model.
2. Gradual Updates for Easier Adoption
One of the biggest challenges with upgrading a major JavaScript framework is the difficulty of migrating large codebases. With React 17, the React team took a more incremental approach, making the upgrade process smoother and less painful for developers.
What Changed?
- No Breaking Changes: React 17 introduces no new breaking changes. Instead, the goal is to ensure that apps can smoothly transition to the new version without needing massive rewrites or changes to existing code.
- Gradual Adoption: React 17 allows for gradual upgrades, meaning that you can mix and match React versions in a single codebase. This is particularly useful for large applications that might be difficult to upgrade all at once. You can upgrade parts of your app to React 17 while keeping other parts on older versions of React until you’re ready for a full migration.
Why It Matters
- Easier Upgrades for Large Applications: This is a game-changer for developers working on large, complex applications with a lot of dependencies. Instead of being forced to upgrade the entire codebase at once, you can slowly adopt React 17 and ensure a more stable transition.
- No More Urgency: For smaller teams or companies that might be hesitant about upgrading, React 17 takes away the urgency. You don’t have to worry about breaking changes disrupting your application.
- Future-Proofing: With this gradual approach, you’ll be able to more easily take advantage of future React features like Concurrent Mode and Server Components without worrying about breaking your entire app.
3. Handling Multiple React Versions in One Project
React 17 introduces a new feature that makes it possible to run multiple versions of React within the same project. This is particularly useful for large projects with many dependencies that might not yet be compatible with the latest version of React.
What Changed?
- React 17 Compatibility Layer: The new compatibility layer allows multiple versions of React to coexist in the same project. This is especially helpful when different parts of your project or different libraries require different versions of React.
- Automatic Handling: React 17 automatically handles the transition between different React versions, so you don’t have to worry about manually managing them.
Why It Matters
- Legacy Support: Many large applications rely on third-party libraries and dependencies that may not be compatible with the latest version of React. This feature makes it much easier to migrate incrementally without breaking everything at once.
- Interoperability: If you’re working in a monorepo or with multiple teams on different parts of a project, this feature makes it easier to run multiple versions of React across different packages or modules. You can now update individual parts of your codebase without worrying about breaking other parts that depend on an older version of React.
4. JSX Transform and No Need for React Imports
Although not a feature specific to React 17, a major change is the new JSX Transform. From React 17 onward, you no longer need to import React in every file that contains JSX.
What Changed?
- The JSX Transform automatically imports the necessary React functions in the background, so you don’t have to explicitly call
import React from 'react'in every component file. This simplifies the codebase, reduces clutter, and makes the React ecosystem more intuitive for newcomers.
Why It Matters
- Cleaner Code: This change reduces boilerplate code, making your codebase cleaner and more readable.
- Faster Development: For new projects, this will speed up development by eliminating the need to add the React import manually.
Conclusion: Why React 17 Matters
React 17 may not come with groundbreaking new features, but it’s an essential release for the future of the framework. By focusing on improving event handling, allowing gradual updates, and enabling multiple React versions in a project, the React team has made it easier for developers to adopt the new version without fear of breaking their apps.
For developers working on large applications, React 17 is a game-changer. It sets the stage for the upcoming Concurrent Mode, allows for seamless upgrades, and ensures smoother compatibility across React versions, all while keeping the developer experience top of mind.
If you’ve been hesitant to upgrade to React 17, this is the perfect time to do so, knowing that it will make managing your codebase simpler and more efficient for years to come.
Feel free to share your thoughts on React 17, or let me know if you have any specific questions about the changes!
