Mastering React Native 0.85: A Guide to the New Animation Backend and Key Updates

Overview

React Native 0.85 marks a significant milestone for mobile development, introducing a revamped animation engine, essential DevTools enhancements, and important ecosystem changes. This guide walks you through the most impactful features—the new Shared Animation Backend, the migration of the Jest preset to a standalone package, Metro TLS support, and DevTools breakthroughs. Whether you're upgrading existing projects or starting fresh, understanding these updates will help you build smoother, more maintainable React Native apps.

Prerequisites

Before diving in, ensure you have:

• A React Native project running version 0.85 or later (the animation backend experimental channel becomes available in 0.85.1).
• Basic familiarity with Animated API and Reanimated concepts.
• Node.js version 18 or newer (older versions are no longer supported).
• For TLS configuration, a basic understanding of Metro bundler settings.

Step-by-Step Instructions

1. Enabling the New Animation Backend

React Native 0.85 (specifically 0.85.1) ships with an experimental Shared Animation Backend, co-developed with Software Mansion. This unifies animation reconciliation for both Animated and Reanimated, unlocking native‑driver support for layout properties like width, height, and flex.

To enable it:

1. Upgrade your app to React Native 0.85.1 or later (npx react-native upgrade).
2. Follow the experimental channel guide to opt into the new backend. Typically this involves setting a flag in your react-native.config.js or environment variable (check official docs for the latest method).

Once active, you can animate layout props using the native driver. Below is a complete example:

import { Animated, Button, View, useAnimatedValue } from 'react-native';

function MyComponent() {
  const width = useAnimatedValue(100);
  const toggle = () => {
    Animated.timing(width, {
      toValue: 300,
      duration: 500,
      useNativeDriver: true,
    }).start();
  };

  return (
    <View style={{flex: 1}}>
      <Animated.View
        style={{
          width,
          height: 100,
          backgroundColor: 'blue',
        }}
      />
      <Button title="Expand" onPress={toggle} />
    </View>
  );
}

This code animates the width from 100 to 300 entirely on the native thread, improving performance significantly. Previously, layout props required JavaScript‑side updates.

2. Migrating the Jest Preset to the New Package

As a breaking change, the Jest preset has been moved from react-native/jest-preset.js to a dedicated package @react-native/jest-preset. If you use Jest for testing, update your configuration:

1. Install the new package: npm install --save-dev @react-native/jest-preset.
2. Modify your jest.config.js (or package.json jest block):
   preset: '@react-native/jest-preset'

Additionally, StyleSheet.absoluteFillObject has been removed. Replace it with {position: 'absolute', top: 0, left: 0, right: 0, bottom: 0}.

3. Configuring Metro with TLS Support

The Metro dev server now accepts a TLS configuration object, allowing HTTPS (and WSS for Fast Refresh) during development. To enable:

1. Generate or obtain a TLS certificate (e.g., via mkcert).
2. Update your metro.config.js:

   module.exports = {
     server: {
       // ...other options
       tlsConfig: {
         cert: '/path/to/cert.pem',
         key: '/path/to/key.pem',
       },
     },
   };

3. Restart the dev server. Your app will now connect securely, useful for testing features like service workers or native modules that require HTTPS.

4. Leveraging DevTools Improvements

React Native DevTools gains three significant enhancements:

• Multiple CDP connections: You can now connect Chrome DevTools, VS Code, and other agents simultaneously without session interruptions. No setup required—just open multiple clients.
• Native tabs on macOS: Build with macOS 26 SDK, the DevTools app supports system‑level tab management. Use Window > Merge All Windows to combine multiple DevTools windows into one.
• Request payload previews: On Android, the Network Panel now displays request body previews (restored after a regression).

These improvements don't require code changes—just upgrade to 0.85 and they're available.

Common Mistakes

Summary

React Native 0.85 introduces a unified animation backend that improves performance for layout properties, a dedicated Jest preset package to streamline testing, Metro TLS support for secure development, and enhanced DevTools with multi‑connection capability, native tabs, and network payload previews. By following the steps above—enabling the experimental backend, migrating to @react-native/jest-preset, configuring TLS, and taking advantage of DevTools updates—you can optimize your development workflow and build more responsive applications. Upgrade today and explore the possibilities!