Config variables for React Native apps

Module to expose config variables to your javascript code in React Native, supporting both iOS and Android.

Bring some 12 factor love to your mobile apps!

Usage

Create a new file .env in the root of your React Native app:

API_URL=https://myapi.com
GOOGLE_MAPS_API_KEY=abcdefgh

Then access variables defined there from your app:

import Config from 'react-native-config'

Config.API_URL  // 'https://myapi.com'
Config.GOOGLE_MAPS_API_KEY  // 'abcdefgh'

Keep in mind this module doesn't obfuscate or encrypt secrets for packaging, so do not store sensitive keys in .env. It's basically impossible to prevent users from reverse engineering mobile app secrets, so design your app (and APIs) with that in mind.

Android

Config variables set in .env are available to your Java classes via BuildConfig:

public HttpURLConnection getApiClient() {
    URL url = new URL(BuildConfig.API_URL);
    // ...
}

You can also read them from your Gradle configuration:

defaultConfig {
    applicationId project.env.get("APP_ID")
}

And use them to configure libraries in AndroidManifest.xml and others:

<meta-data
  android:name="com.google.android.geo.API_KEY"
  android:value="@string/GOOGLE_MAPS_API_KEY" />

All variables are strings, so you may need to cast them. For instance, in Gradle:

versionCode project.env.get("VERSION_CODE").toInteger()

Once again, remember variables stored in .env are published with your code, so DO NOT put anything sensitive there like your app signingConfigs.

iOS

Read variables declared in .env from your Obj-C classes like:

// import header
#import "ReactNativeConfig.h"

// then read individual keys like:
NSString *apiUrl = [ReactNativeConfig envFor:@"API_URL"];

// or just fetch the whole config
NSDictionary *config = [ReactNativeConfig env];

They're also available for configuration in Info.plist, by prepending __RN_CONFIG_ to their name:

__RN_CONFIG_API_URL

Note: Requires specific setup (see below) and a Product > Clean is required after changing the values to see the updated values.

Different environments

Save config for different environments in different files: .env.staging, .env.production, etc.

By default react-native-config will read from .env, but you can change it when building or releasing your app.

The simplest approach is to tell it what file to read with an environment variable, like:

$ ENVFILE=.env.staging react-native run-ios           # bash
$ SET ENVFILE='.env.staging' && react-native run-ios  # windows
$ env:ENVFILE=".env.staging"; react-native run-ios    # powershell

This also works for run-android. Alternatively, there are platform-specific options below.

Android

The same environment variable can be used to assemble releases with a different config:

$ cd android && ENVFILE=.env.staging ./gradlew assembleRelease

Alternatively, you can define a map in build.gradle associating builds with env files. Do it before the apply from call, and use build cases in lowercase, like:

project.ext.envConfigFiles = [
    debug: ".env.development",
    release: ".env.production",
    anothercustombuild: ".env",
]

apply from: project(':react-native-config').projectDir.getPath() + "/dotenv.gradle"

iOS

The basic idea in iOS is to have one scheme per environment file, so you can easily alternate between them.

Start by creating a new scheme:

• In the Xcode menu, go to Product > Scheme > Edit Scheme
• Click Duplicate Scheme on the bottom
• Give it a proper name on the top left. For instance: "Myapp (staging)"

Then edit the newly created scheme to make it use a different env file. From the same "manage scheme" window:

• Expand the "Build" settings on left
• Click "Pre-actions", and under the plus sign select "New Run Script Action"
• Where it says "Type a script or drag a script file", type:

  echo ".env.staging" > /tmp/envfile   # replace .env.staging for your file

This is still a bit experimental and dirty – let us know if you have a better idea on how to make iOS use different configurations opening a pull request or issue!

Setup

Install the package:

$ yarn add react-native-config

Link the library:

$ react-native link react-native-config

Extra step for Android

You'll also need to manually apply a plugin to your app, from android/app/build.gradle:

// 2nd line, add a new apply:
apply from: project(':react-native-config').projectDir.getPath() + "/dotenv.gradle"

Extra step for iOS to support Info.plist

• Go to your project -> Build Settings -> All
• Search for "preprocess"
• Set Preprocess Info.plist File to Yes
• Set Info.plist Preprocessor Prefix File to ${BUILD_DIR}/GeneratedInfoPlistDotEnv.h
• Set Info.plist Other Preprocessor Flags to -traditional
• If you don't see those settings, verify that "All" is selected at the top (instead of "Basic")

Advanced Android Setup

In android/app/build.gradle, if you use applicationIdSuffix or applicationId that is different from the package name indicated in AndroidManifest.xml in <manifest package="..."> tag, for example, to support different build variants: Add this in android/app/build.gradle

defaultConfig {
    ...
    resValue "string", "build_config_package", "YOUR_PACKAGE_NAME_IN_ANDROIDMANIFEST.XML"
}

Troubleshooting

Problems with Proguard

When Proguard is enabled (which it is by default for Android release builds), it can rename the BuildConfig Java class in the minification process and prevent React Native Config from referencing it. To avoid this, add an exception to android/app/proguard-rules.pro:

-keep class com.mypackage.BuildConfig { *; }

mypackage should match the package value in your app/src/main/AndroidManifest.xml file.

Testing

Jest

For mocking the Config.FOO_BAR usage, create a mock at __mocks__/react-native-config.js:

// __mocks__/react-native-config.js
export default {
  FOO_BAR: 'baz',
};