Older versions of React Native’s docs (0.19) recommended running the bundling command manually before building your app if you don’t have a react.gradle file

react-native bundle --platform android --dev false --entry-file index.android.js --bundle-output android/app/src/main/assets/index.android.bundle --assets-dest android/app/src/main/res/

This is tedious and error prone, and where to get the react.gradle file (or what it should contain) is not mentioned

How do we properly hook the bundling task into the normal build process?

Thankfully newer versions of React Native support a better approach

Looking into the react-native directory reveals a Gradle file that defines a bundling task. This is the react.gradle file that is mentioned in the docs.

We just need to hook this Gradle file into our existing build process.

The linked page below describes how to properly build a signed apk

And notice this:

“If you need to change the way the JavaScript bundle and/or drawable resources are bundled (e.g. if you changed the default file/folder names or the general structure of the project), have a look at android/app/build.gradle to see how you can update it to reflect these changes.”

It hints at where to look, but doesn’t do a great job of indicating how to actually configure the project.

Again, the sample project is the key

Look at the sample app’s build.gradle file

Notice the config section

/**
 * The react.gradle file registers a task for each build variant (e.g. bundleDebugJsAndAssets
 * and bundleReleaseJsAndAssets).
 * These basically call `react-native bundle` with the correct arguments during the Android build
 * cycle. By default, bundleDebugJsAndAssets is skipped, as in debug/dev mode we prefer to load the
 * bundle directly from the development server. Below you can see all the possible configurations
 * and their defaults. If you decide to add a configuration block, make sure to add it before the
 * `apply from: "../../node_modules/react-native/react.gradle"` line.
 *
 * project.ext.react = [
 *   // the name of the generated asset file containing your JS bundle
 *   bundleAssetName: "index.android.bundle",
 *
 *   // the entry file for bundle generation
 *   entryFile: "index.android.js",
 *
 *   // whether to bundle JS and assets in debug mode
 *   bundleInDebug: false,
.
.
.
*/

These values allow the customization of the bundle task behavior including:

• • whether to bundle in debug or release builds

• • the path to your React Native project directory

• • the js bundle directory path

• and more…

By customizing these config values in our top level app/build.gradle file, we were able to hook into the bundling command on all our release builds

Our config:

// Configures the bundleJS commands for React-Native
project.ext.react = [

    // whether to bundle JS and assets in debug mode
    bundleInDebug: false,
    // whether to bundle JS and assets in release mode
    bundleInRelease: true, 

    // the root of your RN project, i.e. where "package.json" lives
    root: "path_to_rn_project_directory"
]
apply from: "<path to RN project>/node_modules/react-native/react.gradle"

With this, we can correctly build our signed, release apk with the required React Native js bundle intact

To get started with React Native check out the links below