React v17.0 RC: A Major Leap Forward in Upgrade Experience

A Brief Overview of React

React is a declarative, efficient, and flexible JavaScript library for building user interfaces. With over 156,000 stars on GitHub, it boasts one of the most vibrant frontend communities, building innovative applications.

Upgrading Versions and the Road to v18

Unlike previous releases, React v17.0 RC doesn’t introduce any visible new features. Instead, it focuses on revolutionizing the upgrade experience, making it easier and more seamless for developers to transition between versions. This change in strategy aims to ensure that older versions of React are not left behind, allowing developers to gradually upgrade their applications without worrying about compatibility issues.

Changes to Event Delegation

One of the significant changes in React v17.0 RC is the way event handlers are processed. Previously, event handlers were attached to the document node, but with this new version, they will be attached to the DOM container where the tree was rendered.

// Before
document.addEventListener('click', handleClick);

// After
const rootElement = document.getElementById('root');
rootElement.addEventListener('click', handleClick);

This change enables safer nesting of apps built with different React versions, starting from version 17 and above.

Breaking Changes and Browser Alignment

The new version introduces a few breaking changes, including:

• Changes to event delegation
• Removal of event pooling optimization

Additionally, React’s event system has been aligned more closely with modern browsers, preventing common confusions like firing when scrolling through child elements.

Effect Cleanup Timing and Consistent Errors

React v17.0 RC also brings changes to the useEffect Hook cleanup function timing, making it more consistent and asynchronous.

useEffect(() => {
  // Some effect
  return () => {
    // Cleanup function
  };
}, [dependency]);

Furthermore, the new version ensures consistent errors for returning undefined in functions, including forwardRef and memo components.

Removing Private Exports and Upgrading

Some React internals have been removed, making it incompatible with older React Native for web versions. However, newer versions will be compatible. To upgrade to React v17.0 RC, use the following command:

npm install [email protected] [email protected]

Or, if you’re using Yarn:

yarn add [email protected] [email protected]

For detailed installation instructions, refer to the docs.

What’s Next?

Although React v17.0 RC may not have introduced new features, it sets the stage for version 18, promising a more seamless upgrade experience and closer alignment with modern browsers. As you explore this new version, remember to share your feedback and report any issues on GitHub.