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Prerequisites for Applications

caution

This documentation is still experimental and details are subject to changes as we iterate. Feel free to share your feedback on the discussion inside the working group for this page.

Moreover, it contains several manual steps. Please note that this won't be representative of the final developer experience once the New Architecture is stable. We're working on tools, templates and libraries to help you get started fast on the New Architecture, without having to go through the whole setup.

There are a few prerequisites that should be addressed before the New Architecture is enabled in your application.

Use a React Native >= 0.68 release​

React Native released the support for the New Architecture with the release 0.68.0.

This guide is written with the expectation that you’re using the latest React Native release. At the moment of writing, this is 0.70.0. Other than this guide, you can leverage the upgrade helper to determine what other changes may be required for your project.

To update to the most recent version of React Native, you can run this command:

npx react-native upgrade

Android specifics​

Using the New Architecture on Android has some prerequisites that you need to meet:

  1. Using Gradle 7.x and Android Gradle Plugin 7.x
  2. Using the new React Gradle Plugin
  3. Building react-native from Source

You can update Gradle by running:

cd android && ./gradlew wrapper --gradle-version 7.3.3 --distribution-type=all

While the AGP version should be updated inside the top-level build.gradle file at the com.android.tools.build:gradle dependency line.

Now, you can edit your top-level settings.gradle file to include the following line at the end of the file:

includeBuild('../node_modules/react-native-gradle-plugin')

include(":ReactAndroid")
project(":ReactAndroid").projectDir = file('../node_modules/react-native/ReactAndroid')
include(":ReactAndroid:hermes-engine")
project(":ReactAndroid:hermes-engine").projectDir = file('../node_modules/react-native/ReactAndroid/hermes-engine')

Then, open the android/app/src/main/AndroidManifest.xml file and add this line:

android:windowSoftInputMode="adjustResize"
+ android:exported="true">
<intent-filter>

Then, edit your top-level Gradle file to include the highlighted lines:

buildscript {
    ext {
        buildToolsVersion = "31.0.0"
        minSdkVersion = 21
        compileSdkVersion = 31
        targetSdkVersion = 31
        if (System.properties['os.arch'] == "aarch64") {
            // For M1 Users we need to use the NDK 24 which added support for aarch64
            ndkVersion = "24.0.8215888"
        } else {
            // Otherwise we default to the side-by-side NDK version from AGP.
            ndkVersion = "21.4.7075529"
        }
    }

    // ...
    dependencies {
        // Make sure that AGP is at least at version 7.x
        classpath("com.android.tools.build:gradle:7.2.0")

        // Add those lines
        classpath("com.facebook.react:react-native-gradle-plugin")
        classpath("de.undercouch:gradle-download-task:4.1.2")
    }
}

Edit your module-level Gradle file (usually app/build.gradle[.kts]) to include the following:

// ...

apply plugin: "com.android.application"

// ...

if (enableHermes) {
-    def hermesPath = "../../node_modules/hermes-engine/android/";
-    debugImplementation files(hermesPath + "hermes-debug.aar")
-    releaseImplementation files(hermesPath + "hermes-release.aar")
+    //noinspection GradleDynamicVersion
+    implementation("com.facebook.react:hermes-engine:+") { // From node_modules
+        exclude group:'com.facebook.fbjni'
+    }
} else {

// ...

+ configurations.all {
+     resolutionStrategy.dependencySubstitution {
+         substitute(module("com.facebook.react:react-native"))
+                 .using(project(":ReactAndroid"))
+                 .because("On New Architecture we're building React Native from source")
+         substitute(module("com.facebook.react:hermes-engine"))
+                .using(project(":ReactAndroid:hermes-engine"))
+                .because("On New Architecture we're building Hermes from source")
+     }
+ }

// Run this once to be able to run the application with BUCK
// puts all compile dependencies into folder libs for BUCK to use
task copyDownloadableDepsToLibs(type: Copy) {

// ...

+ def isNewArchitectureEnabled() {
+     // To opt-in for the New Architecture, you can either:
+     // - Set `newArchEnabled` to true inside the `gradle.properties` file
+     // - Invoke gradle with `-newArchEnabled=true`
+     // - Set an environment variable `ORG_GRADLE_PROJECT_newArchEnabled=true`
+     return project.hasProperty("newArchEnabled") && project.newArchEnabled == "true"
+ }

Finally, it’s time to update your project to use the react-native dependency from source, rather than using a precompiled artifact from the NPM package. This is needed as the later setup will rely on building the native code from source.

Let’s edit your module-level build.gradle (the one inside app/ folder) and change the following line:

dependencies {
-  implementation "com.facebook.react:react-native:+"  // From node_modules
+  implementation project(":ReactAndroid")  // From node_modules

Use Hermes​

Hermes is an open-source JavaScript engine optimized for React Native. Hermes is enabled by default and you have to explicitly disable it if you want to use JSC.

We highly recommend using Hermes in your application. With Hermes enabled, you will be able to use the JavaScript debugger in Flipper to directly debug your JavaScript code.

Please follow the instructions on the React Native website to learn how to enable/disable Hermes.

caution

iOS: If you opt out of using Hermes, you will need to replace HermesExecutorFactory with JSCExecutorFactory in any examples used throughout the rest of this guide.

Android​

To enable Hermes in Android, open the android/app/build.gradle and apply the following changes:

project.ext.react = [
-    enableHermes: true,  // clean and rebuild if changing
+    enableHermes: true,  // clean and rebuild if changing
]
// ...

}

if (enableHermes) {
-    def hermesPath = "../../node_modules/hermes-engine/android/";
-    debugImplementation files(hermesPath + "hermes-debug.aar")
-    releaseImplementation files(hermesPath + "hermes-release.aar")
+    //noinspection GradleDynamicVersion
+    implementation("com.facebook.react:hermes-engine:+") { // From node_modules
+        exclude group:'com.facebook.fbjni'
+    }
} else {

Moreover, you'll need to update the proguard-rules, adding the following ones:

-keep class com.facebook.hermes.unicode.** { *; }
-keep class com.facebook.jni.** { *; }

After that, remember to cleanup the project, running

cd android
./gradlew clean

iOS: Make the project build​

After upgrading the project, there are a few changes you need to apply:

  1. Fix an API change in the AppDelegate.m. Open this file and apply this change:
#if DEBUG
-       return [[RCTBundleURLProvider sharedSettings] jsBundleURLForBundleRoot:@"index" fallbackResource:nil];
+       return [[RCTBundleURLProvider sharedSettings] jsBundleURLForBundleRoot:@"index"];
#else
  1. Target the proper iOS version. Open the Podfile and apply this change:
- platform :ios, '11.0'
+ platform :ios, '12.4'
  1. Create an .xcode.env file to export the locaion of the NODE_BINARY. Navigate to the ios folder and run this command:
echo 'export NODE_BINARY=$(command -v node)' > .xcode.env

If you need it, you can also open the file and replace the $(command -v node) with the path to the node executable. React Native supports also a local version of this file .xcode.env.local. This file is not synced with the repository to let you customize your local setup, if it differs from the Continuous Integration or the team one.

iOS: Use Objective-C++ (.mm extension)​

Turbo Native Modules can be written using Objective-C or C++. In order to support both cases, any source files that include C++ code should use the .mm file extension. This extension corresponds to Objective-C++, a language variant that allows for the use of a combination of C++ and Objective-C in source files.

info

Use Xcode to rename existing files to ensure file references persist in your project. You might need to clean the build folder (Project → Clean Build Folder) before re-building the app. If the file is renamed outside of Xcode, you may need to click on the old .m file reference and Locate the new file.

iOS: TurboModules: Ensure your App Provides an RCTCxxBridgeDelegate​

In order to set up the TurboModule system, you will add some code to interact with the bridge in your AppDelegate. Before you start, go ahead and rename your AppDelegate file to use the .mm extension.

Now you will have your AppDelegate conform to RCTCxxBridgeDelegate. Start by adding the following imports at the top of your AppDelegate file:

#import <reacthermes/HermesExecutorFactory.h>
#import <React/RCTCxxBridgeDelegate.h>
#import <React/RCTJSIExecutorRuntimeInstaller.h>

Then, declare your app delegate as a RCTCxxBridgeDelegate provider:

@interface AppDelegate () <RCTCxxBridgeDelegate> {
  // ...
}
@end

To conform to the RCTCxxBridgeDelegate protocol, you will need to implement the jsExecutorFactoryForBridge: method. Typically, this is where you would return a JSCExecutorFactory or HermesExecutorFactory, and we will use it to install our TurboModules bindings later on.

You can implement the jsExecutorFactoryForBridge: method like this:

#pragma mark - RCTCxxBridgeDelegate

- (std::unique_ptr<facebook::react::JSExecutorFactory>)jsExecutorFactoryForBridge:(RCTBridge *)bridge
{
  return std::make_unique<facebook::react::HermesExecutorFactory>(facebook::react::RCTJSIExecutorRuntimeInstaller([bridge](facebook::jsi::Runtime &runtime) {
      if (!bridge) {
        return;
      }
    })
  );
}