The Node.js for Mobile Apps React Native plugin

Installation

$ npm install nodejs-mobile-react-native --save

For iOS, run pod install for linking the native code parts:

$ cd iOS && pod install

iOS

Universal binaries are included in the plugin, so you can run in both iOS simulators and devices.

nodejs-mobile-react-native supports iOS 11.0 or later. In order to archive the application, the deployment target needs to be iOS 11.0 or later.

Android

You may need to open your app's /android folder in Android Studio, so that it detects, downloads and cofigures requirements that might be missing, like the NDK and CMake to build the native code part of the project.

You can also set the environment variable ANDROID_NDK_HOME, as in this example:

export ANDROID_NDK_HOME=/Users/username/Library/Android/sdk/ndk-bundle

Usage

Node.js project

When nodejs-mobile-react-native was installed through npm, it created a nodejs-assets/nodejs-project/ path inside your application. This path will be packaged with your application and the background project will be started using the main.js file inside. It contains a sample-main.js and sample-package.json files under nodejs-assets/nodejs-project/.

The sample-main.js and sample-package.json files contain a sample echo project. We advise to rename sample-main.js to main.js and sample-package.json to package.json to get you started easily.

Attention: The sample-main.js and sample-package.json will be overwritten with installs/updates of nodejs-mobile-react-native.

The sample main.js contents:

var rn_bridge = require('rn-bridge');

// Echo every message received from react-native.
rn_bridge.channel.on('message', (msg) => {
  rn_bridge.channel.send(msg);
} );

// Inform react-native node is initialized.
rn_bridge.channel.send("Node was initialized.");

Recent versions of react-native (since 0.57) throw an error during the bundling of the project. Please look at the Troubleshooting Duplicate module name section for instructions on how to configure the react-native bundler to ignore the nodejs-project folder.

The Node.js runtime accesses files through Unix-based pathnames, so in Android the node project is copied from the project's apk assets into the default application data folder at startup, during the first run or after an update, under nodejs-project/.

Attention: Given the project folder will be overwritten after each application update, it should not be used for persistent storage.

To expedite the process of extracting the assets files, instead of parsing the assets hierarchy, a list of files file.list and a list of folders dir.list are created when the application is compiled and then added to the application assets. On Android 6.x and older versions, this allows to work around a serious perfomance bug in the Android assets manager.

Node Modules

Node modules can be added to the project using npm install inside nodejs-assets/nodejs-project/, as long as there's a package.json already present.

Native Modules

On Linux and macOS, there is support for building modules that contain native code.

The plugin automatically detects native modules inside your nodejs-project folder by searching for .gyp files. It's recommended to have the build prerequisites mentioned in nodejs-mobile for Android and iOS. For Android it's also recommended that you set the ANDROID_NDK_HOME environment variable in your system.

Building native modules for Android can take a long time, since it depends on building a standalone NDK toolchain for each required architecture. The resulting .node binaries are then included in the final application in a separate asset path for each architecture and the correct one will be chosen at runtime.

While the plugin tries to detect automatically the presence of native modules, there's a way to override this detection and turn the native modules build process on or off, by creating the nodejs-assets/BUILD_NATIVE_MODULES.txt file and setting its contents to 1 or 0, respectively. This can be used to start your application like this:

echo "1" > nodejs-assets/BUILD_NATIVE_MODULES.txt
react-native run-android

echo "1" > nodejs-assets/BUILD_NATIVE_MODULES.txt
react-native run-ios

React-Native application

To communicate with Node.js from your react-native application, first import nodejs-mobile-react-native.

import nodejs from 'nodejs-mobile-react-native';

Then add this to your Application's main component's componentWillMount lifecycle event:

  componentWillMount()
  {
    nodejs.start("main.js");
    nodejs.channel.addListener(
      "message",
      (msg) => {
        alert("From node: " + msg);
      },
      this
    );
  }

This will tell the native code to start a dedicated thread running Node.js starting at the main.js file in nodejs-assets/nodejs-project/, as described above. It will then register a listener to show alert boxes with each message sent from Node.js.

Attention: The Node.js project runs on a dedicated thread and as a singleton, so only the first nodejs.start() command will make any effect, as further calls will not start new threads. This means that if you use react-native's hotreload functionality you won't see any changes in the Node.js project.

We can then define a button in our interface to send messages to our Node.js project:

  <Button title="Message Node"
    onPress={() => nodejs.channel.send('A message!')}
    />

Methods available in the React Native layer

These methods can be called from the React Native javascript code directly:

import nodejs from 'nodejs-mobile-react-native';

• nodejs.start
• nodejs.startWithScript
• nodejs.channel.addListener
• nodejs.channel.post
• nodejs.channel.send

nodejs.channel.send(...msg) is equivalent to nodejs.channel.post('message', ...msg). It is maintained for backward compatibility purposes.

The nodejs.channel object inherits from React Native's EventEmitter class, with emit removed and post and send added.

nodejs.start(scriptFileName [, options])

Param	Type
scriptFileName	string
options	StartupOptions

Starts the nodejs-mobile runtime thread with a file inside the nodejs-project directory.

nodejs.startWithScript(scriptBody [, options])

Param	Type
scriptBody	string
options	StartupOptions

Starts the nodejs-mobile runtime thread with a script body.

nodejs.channel.addListener(event, callback)

Param	Type
event	string
callback	function

Registers a callback for user-defined events raised from the nodejs-mobile side.

nodejs.channel.post(event, ...message)

Param	Type
event	string
...message	any JS type that can be serialized with JSON.stringify and deserialized with JSON.parse

Raises a user-defined event on the nodejs-mobile side.

nodejs.channel.send(...message)

Param	Type
...message	any JS type that can be serialized with JSON.stringify and deserialized with JSON.parse

Raises a 'message' event on the nodejs-mobile side. It is an alias for nodejs.channel.post('message', ...message);.

StartupOptions: object

Name	Type	Default	Description
redirectOutputToLogcat	boolean	true	Allows to disable the redirection of the Node stdout/stderr to the Android logcat

Methods available in the Node layer

The following methods can be called from the Node javascript code through the rn-bridge module:

  const rn_bridge = require('rn-bridge');

• rn_bridge.channel.on
• rn_bridge.channel.post
• rn_bridge.channel.send
• rn_bridge.app.on
• rn_bridge.app.datadir

rn_bridge.channel.send(...msg) is equivalent to rn_bridge.channel.post('message', ...msg). It is maintained for backward compatibility purposes.

The rn_bridge.channel object inherits from Node's EventEmitter class, with emit removed and post and send added.

rn_bridge.channel.on(event, callback)

Param	Type
event	string
callback	function

Registers a callback for user-defined events raised from the React Native side.

To receive messages from nodejs.channel.send, use:

  rn_bridge.channel.on('message', listenerCallback);

rn_bridge.channel.post(event, ...message)

Param	Type
event	string
...message	any JS type that can be serialized with JSON.stringify and deserialized with JSON.parse

Raises a user-defined event on the React Native side.

rn_bridge.channel.send(...message)

Param	Type
...message	any JS type that can be serialized with JSON.stringify and deserialized with JSON.parse

Raises a 'message' event on the React Native side. It is an alias for rn_bridge.channel.post('message', ...message);.

rn_bridge.app.on(event, callback)

Param	Type
event	string
callback	function

Registers callbacks for App events. Currently supports the 'pause' and 'resume' events, which are raised automatically when the app switches to the background/foreground.

rn_bridge.app.on('pause', (pauseLock) => {
  console.log('[node] app paused.');
  pauseLock.release();
});
rn_bridge.app.on('resume', () => {
  console.log('[node] app resumed.');
});

The 'pause' event is raised when the application switches to the background. On iOS, the system will wait for the 'pause' event handlers to return before finally suspending the application. For the purpose of letting the iOS application know when it can safely suspend after going to the background, a pauseLock argument is passed to each 'pause' listener, so that release() can be called on it to signal that listener has finished doing all the work it needed to do. The application will only suspend after all the locks have been released (or iOS forces it to).

rn_bridge.app.on('pause', (pauseLock) => {
  server.close( () => {
    // App will only suspend after the server stops listening for connections and current connections are closed.
    pauseLock.release();
  });
});

Warning : On iOS, the application will eventually be suspended, so the pause event should be used to run the clean up operations as quickly as possible and let the application suspend after that. Make sure to call pauseLock.release() in each 'pause' event listener, or your Application will keep running in the background for as long as iOS will allow it.

rn_bridge.app.datadir()

Returns a writable path used for persistent data storage in the application. Its value corresponds to NSDocumentDirectory on iOS and FilesDir on Android.

Channel callback: function(arg)

Name	Type
arg	any JS type that can be serialized with JSON.stringify and deserialized with JSON.parse

The messages sent through the channel can be of any type that can be correctly serialized with JSON.stringify on one side and deserialized with JSON.parse on the other side, as it is what the channel does internally. This means that passing JS dates through the channel will convert them to strings and functions will be removed from their containing objects. In line with The JSON Data Interchange Syntax Standard, the channel supports sending messages that are composed of these JS types: Boolean, Number, String, Object, Array.

Notes about other node APIs

os.tmpdir()

On iOS, os.tmpdir() returns a temporary directory, since iOS sets the TMPDIR environment variable of the application to the equivalent of calling NSTemporaryDirectory.

The Android OS doesn't define a temporary directory for the system or application, so the plugin sets the TMPDIR environment variable to the value of the application context's CacheDir value.

Troubleshooting

On Android applications, the react-native build process is sometimes unable to rebuild assets. If you are getting errors while building the application using react-native run-android, the following commands can help you do a clean rebuild of the project, when run in your project's folder.

On Windows:

cd android
gradlew clean
cd ..
react-native run-android

On Linux/macOS:

cd android
./gradlew clean
cd ..
react-native run-android

Duplicate module name

During the react-native application's build process, the nodejs-project gets copied to the application's assets, where they'll be used by nodejs-mobile. The react-native packager monitors the project's folder for javascript packages and may throw a "jest-haste-map: Haste module naming collision" error.

To avoid this error, instruct the react-native packager to ignore the nodejs-project and the platform folders where it is copied to. Edit the metro.config.js file in your react-native project's root path with the following contents if you're using recent versions of react-native (>= v0.60) and add the blacklist require and the following resolver to the module exports:

const blacklist = require('metro-config/src/defaults/blacklist');

module.exports = {
  resolver: {
    blacklistRE: blacklist([
      /\/nodejs-assets\/.*/,
      /\/android\/.*/,
      /\/ios\/.*/
    ])
  },

...

};

Changelog

Releases are documented in CHANGELOG.md