Last week at Chain React we announced Hermes, an open source JavaScript engine we’ve been working on at Facebook. It’s a small and lightweight JavaScript engine optimized for running React Native on Android. Check it out!

Hermes improves React Native performance by decreasing memory utilization, reducing download size, and decreasing the time it takes for the app to become usable or “time to interactive” (TTI).

“As we analyzed performance data, we noticed that the JavaScript engine itself was a significant factor in startup performance and download size. With this data in hand, we knew we had to optimize JavaScript performance in the more constrained environments of a mobile phone compared with a desktop or laptop. After exploring other options, we built a new JavaScript engine we call Hermes. It is designed to improve app performance, focusing on our React Native apps, even on mass-market devices with limited memory, slow storage, and reduced computing power.” —Hermes: An open source JavaScript engine optimized for mobile apps, starting with React Native

Want to get started right away? Be sure to check out our new guide to enabling Hermes in your existing React Native app in the docs!

Illustration by Rachel Nabors

We’re excited to announce React Native 0.61, which includes a new reloading experience we’re calling Fast Refresh.

Fast Refresh​

When we asked the React Native community about common pain points, one of the top answers was that the “hot reloading” feature was broken. It didn’t work reliably for function components, often failed to update the screen, and wasn’t resilient to typos and mistakes. We heard that most people turned it off because it was too unreliable.

In React Native 0.61, we’re unifying the existing “live reloading” (reload on save) and “hot reloading” features into a single new feature called “Fast Refresh” . Fast Refresh was implemented from scratch with the following principles:

• Fast Refresh fully supports modern React , including function components and Hooks.
• Fast Refresh gracefully recovers after typos and other mistakes, and falls back to a full reload when needed.
• Fast Refresh doesn’t perform invasive code transformations so it’s reliable enough to be on by default.

To see Fast Refresh in action, check out this video:

Give it a try, and let us know what you think! If you prefer, you can turn it off in the Dev Menu (Cmd+D on iOS, Cmd+M or Ctrl+M on Android). Turning it on and off is instant so you can do it any time.

Here are a few Fast Refresh tips:

• Fast Refresh preserves React local state in function components (and Hooks!) by default.
• If you need to reset the React state on every edit, you can add a special // @refresh reset comment to the file with that component.
• Fast Refresh always remounts class components without preserving state. This ensures it works reliably.
• We all make mistakes in the code! Fast Refresh automatically retries rendering after you save a file. You don't need to reload the app manually after fixing a syntax or a runtime error.
• Adding a console.log or a debugger statement during edits is a neat debugging technique.

Please report any issues with Fast Refresh on GitHub, and we’ll look into them.

Other Improvements​

• Fixed use_frameworks! CocoaPods support. In 0.60 we made some updates to integrate CocoaPods by default. Unfortunately, this broke builds using use_frameworks!. This is fixed in 0.61, making it easier to integrate React Native into your iOS projects that require building with dynamic frameworks.
• Add useWindowDimensions Hook. This new Hook automatically provides and subscribes to dimension updates, and can be used instead of the Dimensions API in most cases.
• React was upgraded to 16.9. This version deprecates old names for the UNSAFE _ lifecycle methods, contains improvements to act , and more. See the React 16.9 blog post for an automated migration script and more information.

Breaking Changes​

• Remove React .xcodeproj. In 0.60, we introduced auto-linking support via CocoaPods. We have also integrated CocoaPods into the e2e tests runs, so that from now on, we have a unified standard way of integrating RN into iOS apps. This effectively deprecates the React .xcodeproj support, and the file has been removed starting 0.61. Note: if you use 0.60 auto-linking already, you shouldn't be affected.

Thanks​

Thanks to all of the contributors that helped make 0.61 possible!

To see all the updates, take a look at the 0.61 changelog.

After over 20 pull requests from 6 contributors in the React Native Community, we're excited to launch react-native doctor , a new command to help you out with getting started, troubleshooting and automatically fixing errors with your development environment. The doctor command is heavily inspired by Expo and Homebrew's own doctor command with a pinch of UI inspired by Jest.

Here it is in action:

How it works​

The doctor command currently supports most of the software and libraries that React Native relies on, such as CocoaPods, Xcode and Android SDK. With doctor we'll find issues with your development environment and give you the option to automatically fix them. If doctor is not able to fix an issue, it will display a message and a helpful link explaining how to fix it manually as the following:

Try it now​

The doctor command is available as a part of React Native 0.62. However, you can try it without upgrading yet:

npx @react-native-community/cli doctor

What checks are currently supported​

doctor currently supports the following checks:

• Node.js (>= 8.3)
• yarn (>= 1.10)
• npm (>= 4)
• Watchman (>= 4), used for watching changes in the filesystem when in development mode.

Specific to the Android environment:

• Android SDK (>= 26), the software runtime for Android.
• Android NDK (>= 19), the native development toolkit for Android.
• ANDROID_HOME , environment variable required by the Android SDK setup.

And to the iOS environment:

• Xcode (>= 10), IDE for developing, building and shipping iOS applications.
• CocoaPods, library dependency management tool for iOS applications.
• ios-deploy (optional), library used internally by the CLI to install applications on a physical iOS device.

Thanks​

Huge thanks for the React Native Community for working on this, in particular @thymikee, @thib92, @jmeistrich, @tido64 and @rickhanlonii.

Today we’re releasing React Native version 0.62 which includes support for Flipper by default.

This release comes in the midst of a global pandemic. We’re releasing this version today to respect the work of hundreds of contributors who made this release possible and to prevent the release from falling too far behind master. Please be mindful of the reduced capacity of contributors to help with issues and prepare to delay upgrading if necessary.

Flipper by default​

Flipper is a developer tool for debugging mobile apps. It’s popular in the Android and iOS communities, and in this release we’ve enabled support by default for new and existing React Native apps.

Flipper provides the following features out of the box:

• Metro Actions : Reload the app and trigger the Dev Menu right from the toolbar.
• Crash Reporter : View crash reports from Android and iOS devices.
• React DevTools : Use the newest version of React DevTools right alongside all your other tools.
• Network Inspector : View all of the network requests made by device applications.
• Metro and Device Logs : View, search, and filter all logs from both Metro and the Device.
• Native Layout Inspector : View and edit the native layout output by the React Native renderer.
• Database and Preference Inspectors : View and edit the device databases and preferences.

Additionally, since Flipper is an extensible platform, it provides a marketplace that pulls plugins from NPM so you can publish and install custom plugins specific to your workflows. See the available plugins here.

For more information, check out the Flipper documentation.

New dark mode features​

We’ve added a new Appearance module to provide access to the user's appearance preferences, such as their preferred color scheme (light or dark).

const colorScheme = Appearance.getColorScheme();
if (colorScheme === 'dark') {
  // Use dark color scheme
}

We’ve also added a hook to subscribe to state updates to the users preferences:

import {Text, useColorScheme} from 'react-native';

const MyComponent = () => {
  const colorScheme = useColorScheme();
  return <Text>useColorScheme(): {colorScheme}</Text>;
};

See the docs for Appearance and useColorScheme for more information.

Moving Apple TV to react-native-tvos​

As part of our Lean Core effort and to bring Apple TV in line with other platforms like React Native Windows and React Native macOS, we’ve started to remove Apple TV specific code from core.

Going forward, Apple TV support for React Native will be maintained in react-native-community/react-native-tvos along with the corresponding react-native-tvos NPM package. This is a full fork of the main repository, with only the changes needed to support Apple TV.

Releases of react-native-tvos will be based on the public release of React Native. For this 0.62 release of react-native please upgrade Apple TV projects to use react-native-tvos 0.62.

More upgrade support​

When 0.61 was released, the community introduced a new upgrade helper tool to support developers upgrading to new versions of React Native. The upgrade helper provides a diff of changes from the version you're on to the version you're targeting, allowing you to see the changes that need to be made for your specific upgrade.

Even with this tool, issues come up when upgrading. Today we're introducing more dedicated upgrading support by announcing Upgrade-Support. Upgrade Support is a GitHub issue tracker where users can submit issues specific to upgrading their projects to receive help from the community.

We're always working to improve the upgrade experience, and we hope that these tools give users the support they need in the edge cases we haven't covered yet.

Other improvements​

• LogBox : We’re adding the new LogBox error and warning experience as an opt-in; to enable it, add require('react-native').unstable_enableLogBox() to your index.js file.
• React DevTools v4 : This change includes an upgrade to the latest React DevTools which offers significant performance gains, an improved navigation experience, and full support for React Hooks.
• Accessibility improvements : We’ve made improvements to accessibility including adding accessibilityValue, missing props on Touchables, onSlidingComplete accessibility events, and changing the default role of Switch component from "button" to "switch" .

Breaking changes​

• Remove PropTypes : We're removing propTypes from core components in order to reduce the app size impact of React Native core and to favor static type systems which check at compile time instead of runtime.
• Remove accessibilityStates : We’ve removed the deprecated accessibilityStates property in favor of the new accessibilityState prop which is a more semantically rich way for components to describe information about their state to accessibility services.
• TextInput changes : We removed onTextInput from TextInput as it’s uncommon, not W3C compliant, and difficult to implement in Fabric. We also removed the undocumented inputView prop, and selectionState .

Deprecations​

• AccessibilityInfo.fetch was already deprecated, but in this release we added a warning.
• Setting useNativeDriver is now required to support switching the default in the future.
• The ref of an Animated component is now the internal component and deprecated getNode .

Thanks​

Thank you to the hundreds of contributors that helped make 0.62 possible!

To see all the updates, take a look at the 0.62 changelog.

Today we’re releasing React Native 0.63 that ships with LogBox turned on by default.

LogBox​

We’ve heard frequent feedback from the community that errors and warnings are difficult to debug in React Native. To address these issues we took a look at the entire error, warning, and log system in React Native and redesigned it from the ground up.

LogBox is a completely redesigned redbox, yellowbox, and logging experience in React Native. In 0.62 we introduced LogBox as an opt-in. In this release, we’re launching LogBox as the default experience in all of React Native.

LogBox addresses complaints that errors and warnings were too verbose, poorly formatted, or unactionable by focusing on three primary goals:

• Concise : Logs should provide the minimum amount of information necessary to debug an issue.
• Formatted : Logs should be formatted so that you can quickly find the information you need.
• Actionable : Logs should be actionable, so you can fix the issue and move on.

To achieve these goals, LogBox includes:

• Log notifications : We’ve redesigned the warning notifications and added support for errors so that all console.warn and console.log messages show up as notifications instead of covering your app.
• Code Frames : Every error and warning now includes a code frame that shows the source code of the log right inside the app, allowing you to quickly identify the source of your issue.
• Component Stacks : All component stacks are now stripped from error messages and put into their own section with the top three frames visible. This gives you a single, consistent space to expect stack frame information that doesn’t clutter the log message.
• Stack Frame Collapsing : By default we now collapse call stack frames not related to your application’s code so you can quickly see the issue in your app and not sift through React Native internals.
• Syntax Error Formatting : We’ve improved the formatting for syntax errors and added codeframes with syntax highlighting so you can see the source of the error, fix it, and continue coding without React Native getting in your way.

We’ve wrapped all of these features into an improved visual design that’s consistent between errors and warnings and allows paginating through all logs in one enjoyable UI.

With this change we’re also deprecating YellowBox in favor of LogBox APIs:

• LogBox.ignoreLogs() : This function replaces YellowBox.ignoreLogs([]) as a way to silence any logs that match the given strings or regexes.
• LogBox.ignoreAllLogs() : This function replaces console.disableYellowBox as a way to turn off error or warning notifications. Note: this only disables notifications, uncaught errors will still open a full screen LogBox.

In 0.63, we will warn when using these deprecated modules or methods. Please update your call sites off of these APIs before they are removed in 0.64.

For more information on LogBox and debugging react native, see the docs here.

Pressable​

React Native is built to enable applications to meet user’s expectations of the platform. This includes avoiding “tells”—little things that give away that the experience was built with React Native. One major source of these tells has been the Touchable components: Button , TouchableWithoutFeedback , TouchableHighlight , TouchableOpacity , TouchableNativeFeedback , and TouchableBounce . These components make your application interactive by allowing you to provide visual feedback to user interactions. However, because they include built-in styles and effects that don’t match the platform interaction, users can tell when experiences are written with React Native.

Further, as React Native has grown and our bar for high-quality applications has gone up, these components haven't grown with it. React Native now supports platforms like Web, Desktop, and TV, but support for additional input modalities has been lacking. React Native needs to support high-quality interaction experiences on all platforms.

To address these problems, we are shipping a new core component called Pressable . This component can be used to detect various types of interactions. The API was designed to provide direct access to the current state of interaction without having to maintain state manually in a parent component. It was also designed to enable platforms to extend it's capabilities to include hover, blur, focus, and more. We expect that most people will build and share components utilizing Pressable under the hood instead of relying on the default experience of something like TouchableOpacity .

import {Pressable, Text} from 'react-native';

<Pressable
  onPress={() => {
    console.log('pressed');
  }}
  style={({pressed}) => ({
    backgroundColor: pressed ? 'lightskyblue' : 'white',
  })}>
  <Text style={styles.text}>Press Me!</Text>
</Pressable>;

A simple example of a Pressable component in action

You can learn more about it from the documentation.

Native Colors (PlatformColor, DynamicColorIOS)​

Every native platform has the concept of system-defined colors. Colors that automatically respond to system theme settings such as Light or Dark mode, accessibility settings such as a High Contrast mode, and even its context within the app such as the traits of a containing view or window.

While it is possible to detect some of these settings via the Appearance API and/or AccessibilityInfo and set your styles accordingly, such abstractions are not only costly to develop but are approximating the appearance of native colors. These inconsistencies are particularly noticeable when working on a hybrid application, where React Native elements co-exist next to the native ones.

React Native now provides an out-of-the-box solution to use these system colors. PlatformColor() is a new API that can be used like any other color in React Native.

For example, on iOS, the system provides a color called labelColor . That can be used in React Native with PlatformColor like this:

import {Text, PlatformColor} from 'react-native';

<Text style={{color: PlatformColor('labelColor')}}>
  This is a label
</Text>;

Sets the color of the Text component to labelColor as defined by iOS.

Android, on the other hand, provides colors like colorButtonNormal. You can use this color in React Native with:

import {View, Text, PlatformColor} from 'react-native';

<View
  style={{
    backgroundColor: PlatformColor('?attr/colorButtonNormal'),
  }}>
  <Text>This is colored like a button!</Text>
</View>;

Sets the background color of the View component to colorButtonNormal as defined by Android.

You can learn more about PlatformColor from the documentation. You can also check the actual code examples present in the RNTester.

DynamicColorIOS is an iOS only API that lets you define which color to use in light and dark mode. Similar to PlatformColor , this can be used anywhere you can use colors. DynamicColorIOS uses iOS’s colorWithDynamicProvider under the hood.

import {Text, DynamicColorIOS} from 'react-native';

const customDynamicTextColor = DynamicColorIOS({
  dark: 'lightskyblue',
  light: 'midnightblue',
});

<Text style={{color: customDynamicTextColor}}>
  This color changes automatically based on the system theme!
</Text>;

Changes the text color based on the system theme

You can learn more about DynamicColorIOS from the documentation.

Dropping iOS 9 and Node.js 8 support​

After over four years from its release, we are dropping support for iOS 9. This change will allow us to move faster by being able to reduce the number of compatibility checks that need to be placed in the native code to detect whether a given feature was supported on a certain iOS version. With its market share of 1%, it shouldn’t have much negative impact on your customers.

At the same time, we are dropping support for Node 8. Its LTS maintenance cycle expired in December 2019. The current LTS is Node 10 and it is now the version that we are targeting. If you are still using Node 8 for the development of React Native applications, we encourage you to upgrade in order to receive all the latest security fixes and updates.

Other notable improvements​

• Support rendering <View /> in <Text /> without explicit size : You can now render any <View /> inside any <Text /> component without setting its width and height explicitly, which wasn’t always possible. On previous releases of React Native, this would result in a RedBox.
• Changed iOS LaunchScreen from xib to storyboard : Starting April 30, 2020, all apps submitted to the App Store must use an Xcode storyboard to provide the app’s launch screen and all iPhone apps must support all iPhone screens. This commit adjusts the default React Native template to be compatible with this requirement.

Thanks​

Thank you to the hundreds of contributors that helped make 0.63 possible!

Special thanks to Rick Hanlon for authoring the section on LogBox and Eli White for authoring the Pressable part of this article.

To see all the updates, take a look at the 0.63 changelog.