Expo Client

Expo is a set of tools, libraries, and services that let you build native iOS and Android apps by writing JavaScript. This repository is where the Expo client software is developed, and includes the client apps, modules, apps, and more.

Click here to view our documentation for developing on Expo. If you're new to the Expo community, click here to view the Expo Community Guidelines. Thank you for helping keep the Expo community open and welcoming!

Introduction

This is the source code for the Expo client app used to view experiences published to the Expo service. If you want to build and install the Expo client directly onto a device, you're in the right place. Note that if you just want to install the Expo client app on a simulator, you do not need to build it from source. Instead, you should follow the instructions here.

To build the Expo client app, follow the instructions in the Set Up section below. Use the expo-cli command line to use Expo's infrastructure to build your app.

Please ask us on the forums if you get stuck.

Disclaimers:

If you want to build a standalone app that has a custom icon and name, see our documentation here. You're in the wrong place, you shouldn't need to build the Expo clients from source.

If you need to make native code changes to your Expo project, such as adding custom native modules, we can generate a native project for you. You're in the wrong place, you shouldn't need to build the Expo clients from source.

Set Up

Note: We support building the clients only on macOS.

• Install nix (currently curl https://nixos.org/nix/install | sh)
• Install direnv (to do this with nix, run nix-env -iA nixpkgs.direnv)
• Clone this repo; we recommend cloning it to a directory whose full path does not include any spaces (you should clone all the submodules with git clone --recurse-submodules)
• Run yarn in the tools-public directory.

iOS

• Make sure you have latest non-beta Xcode installed.
• Run git lfs pull.
• Run ./generate-files-ios.js in the tools-public directory.
• Open and run ios/Exponent.xcworkspace in Xcode.

Android

• Make sure you have Android Studio 3 installed
• Run android/install-ndk-17c.sh to get the required version of the Android NDK.
• See "Running on a Device"

Running on a Device

iOS

• In Xcode's menu bar, open the Xcode drop-down menu, and select Preferences. Then in the Accounts tab of the preferences menu, add your personal or team apple developer account.
• Connect your test device to your computer with a USB cable.
• In Xcode's menu bar, open the Product drop-down menu, select Destination, then in the Device grouping select your device.
• In the project navigator, select the Exponent project to bring up the project's settings, and then:
  • In the General tab, in the Identity section, put in a unique Bundle Identifier.
  • Also in the General tab, in the Signing section, select your personal or team apple developer account as your Team, and create a new signing certificate by clicking Fix Issue.
• Finally, run the build

Android

• If the Play Store version of the Expo Client App is installed on your test device, uninstall it.
• Connect your test device to your computer with a USB cable.
• Run fastlane android start, or alternately open the android directory in Android Studio, start it, and in the Select Deployment Target dialog, select your device.

Standalone Apps

If you don't need custom native code outside of the Expo SDK, head over to our documentation on building standalone apps without needing Android Studio and Xcode.

If you're still here, make sure to follow the Configure app.json section of the docs before continuing. You'll need to add the appropriate fields to your app.json before the standalone app scripts can run. Once that's done, continue on to the platform-specific instructions.

Android

The Android standalone app script creates a new directory android-shell-app with the modified Android project in it. It then compiles that new directory giving you a signed or unsigned .apk depending on whether you provide a keystore and the necessary passwords. If there are issues with the app you can open the android-shell-app project in Android Studio to debug.

Here are the steps to build a standalone Android app:

• Publish your experience with Expo CLI. Note the published URL.
• cd tools-public.
• If you want a signed .apk, run gulp android-shell-app --url [the published experience url] --sdkVersion [sdk version of your experience] --keystore [path to keystore] --alias [keystore alias] --keystorePassword [keystore password] --keyPassword [key password] --workingDir=../.
• If you don't want a signed .apk, run gulp android-shell-app --url [the published experience url] --sdkVersion [sdk version of your experience] --workingDir=../.
• The .apk file will be at /tmp/shell-signed.apk for a signed .apk or at /tmp/shell-debug.apk for an unsigned .apk.
• adb install the .apk file to test it.
• Upload to the Play Store!

iOS

The iOS standalone app script has two actions, build and configure. build creates an archive or a simulator build of the Expo iOS workspace. configure accepts a path to an existing archive and modifies all its configuration files so that it will run as a standalone Expo experience rather than as the Expo client app.

Here are the steps to build a standalone iOS app:

• Publish your experience with Expo CLI. Note the published URL.
• cd tools-public.
• gulp ios-shell-app --action build --type [simulator or archive] --configuration [Debug or Release]
• The resulting archive will be created at ../shellAppBase-[type].
• gulp ios-shell-app --url [the published experience url] --action configure --type [simulator or archive] --archivePath [path to ExpoKitApp.app] --sdkVersion [sdk version of your experience] --output your-app.tar.gz
• This bundle is not signed and cannot be submitted to iTunes Connect as-is; you'll need to manually sign it if you'd like to submit it to Apple. Fastlane is a good option for this. Also, Expo will do this for you if you don't need to build this project from source.
• If you created a simulator build in the first step, unpack the tar.gz using tar -xvzf your-app.tar.gz. Then you can run this on iPhone Simulator using xcrun simctl install booted <app path> and xcrun simctl launch booted <app identifier>. Another alternative which some people prefer is to install the ios-sim tool and then use ios-sim launch <app path>.
• There are a few more optional flags you can pass to this script. They are all documented in the block comments inside xdl/src/detach/IosShellApp.js.

Modifying JS Code

The Expo client apps run a root Expo project in addition to native code. By default this will use a published version of the project, so any changes made in the home directory will not show up without some extra work.

Serve this project locally by running expo start from the home directory. On iOS, you'll additionally need to set DEV_KERNEL_SOURCE to LOCAL in EXBuildConstants.plist (the default is PUBLISHED).

The native Android Studio and XCode projects have a build hook which will find this if expo start is running. Keep this running and rebuild the app on each platform.

Project Layout

• android contains the Android project.
• home contains the JavaScript source code of the app.
• ios contains the iOS project.
• ios/Exponent.xcworkspace is the Xcode workspace. Always open this instead of Exponent.xcodeproj because the workspace also loads the CocoaPods dependencies.
• tools-public contains build and configuration tools.
• template-files contains templates for files that require private keys. They are populated using the keys in template-files/keys.json.
• template-files/ios/dependencies.json specifies the CocoaPods dependencies of the app.

Tests

iOS

For native XCTest unit tests:

• Press Command+U in XCode to build and test the Tests unit test target.
• Alternatively, run fastlane ios test from the parent directory of ios.

For JS integration tests, test the ExponentIntegrationTests target (not included in the default test scheme). This target requires you to configure EXTestEnvironment.plist with a key testSuiteUrl whose value is the URL to load some version of Expo's test-suite app. This will run a bunch of Jasmine tests against the Expo SDK.

Contributing

Foundation Unimodules

The Foundation Unimodules by Expo are under packages, along with other JS packages. Each Unimodule has its own tests in its package (yarn test) and under apps/test-suite (run a development build of the Expo client, run expo start in test-suite, and load it on a device). We recommend reading the source for several Unimodules to get a sense of the code conventions and taste.

• Guide to Unimodule Development
• Contributing to Expo in General
• Expo JS Style Guide (also mostly applies to TypeScript)

Expo client

Please check with us before putting work into a Pull Request! We don't yet have a good guide available that covers the nuances of how to work with the Expo client so you will want a direct line of communication with someone on the team to ask us questions. The best place to talk to us is either on Slack at https://slack.expo.io or the forums at https://forums.expo.io.

License

The Expo source code is made available under the MIT license. Some of the dependencies are licensed differently, with the BSD license, for example.