This project was bootstrapped with Expo.

Below you'll find information about performing common tasks.

Table of Contents

• Table of Contents
• Updating to New Releases
• Available Scripts
  • npm start
    • npm test
    • npm run ios
    • npm run android
      • Using Android Studio's adb
      • Using Genymotion's adb
    • npm run eject
• Customizing App Display Name and Icon
• Writing and Running Tests
• Environment Variables
  • Configuring Packager IP Address
• Sharing and Deployment
  • Publishing to Expo's React Native Community
• Troubleshooting
  • Networking
  • iOS Simulator won't open
  • QR Code does not scan

Updating to New Releases

Upgrading to a new version of React Native requires updating the react-native, react, and expo package versions, and setting the correct sdkVersion in app.json. See the versioning guide for up-to-date information about package version compatibility. It is highly recommended that you keep the Expo dependency up to date since updating requires that you step through and test each major version including reading the change log and making any specified code changes.

Available Scripts

If Yarn was installed when the project was initialized, then dependencies will have been installed via Yarn, and you should probably use it to run these commands as well. Unlike dependency installation, command running syntax is identical for Yarn and NPM at the time of this writing.

npm start

Runs your app in development mode.

Open it in the Expo app on your phone to view it. It will reload if you save edits to your files, and you will see build errors and logs in the terminal.

Sometimes you may need to reset or clear the React Native packager's cache. To do so, you can pass the --reset-cache flag to the start script:

npm start -- --reset-cache
# or
yarn start -- --reset-cache

npm test

Runs the jest test runner on your tests.

npm run ios

Like npm start, but also attempts to open your app in the iOS Simulator if you're on a Mac and have it installed.

npm run android

Like npm start, but also attempts to open your app on a connected Android device or emulator if you have it installed.

Using Android Studio's adb

1. Make sure that you can run adb from your terminal.
2. Open Genymotion and navigate to Settings -> ADB. Select “Use custom Android SDK tools” and update with your Android SDK directory.

Using Genymotion's adb

1. Find Genymotion’s copy of adb. On macOS for example, this is normally /Applications/Genymotion.app/Contents/MacOS/tools/.
2. Add the Genymotion tools directory to your path (instructions for Mac, Linux, and Windows).
3. Make sure that you can run adb from your terminal.

npm run eject

This will start the process of "ejecting" from Expo's managed workflow build scripts. You'll be asked a couple of questions about how you'd like to build your project.

Warning: Running eject is a permanent action (aside from whatever version control system you use). An ejected app will require you to have an Xcode and/or Android Studio environment set up.

Customizing App Display Name and Icon

You can edit app.json to include many configuration keys. Please see the linked documentation for the various settings that are available.

Writing and Running Tests

This project is set up to use jest for tests. You can configure whatever testing strategy you like, but jest works out of the box. Create test files in directories called __tests__ or with the .test extension to have the files loaded by jest. See the the template project for an example test. The jest documentation is also a wonderful resource, as is the React Native testing tutorial.

Environment Variables

You can configure some of Expo's behavior using environment variables.

Configuring Packager IP Address

When starting your project, you'll see something like this for your project URL:

exp://192.168.0.2:19000

The "manifest" at that URL tells the Expo app how to retrieve and load your app's JavaScript bundle, so even if you load it in the app via a URL like exp://localhost:19000, the Expo client app will still try to retrieve your app at the IP address that the start script provides.

In some cases, this is less than ideal. This might be the case if you need to run your project inside of a virtual machine and you have to access the packager via a different IP address than the one which prints by default. In order to override the IP address or hostname that is detected by Create React Native App, you can specify your own hostname via the REACT_NATIVE_PACKAGER_HOSTNAME environment variable:

Mac and Linux:

REACT_NATIVE_PACKAGER_HOSTNAME='my-custom-ip-address-or-hostname' npm start

Windows:

set REACT_NATIVE_PACKAGER_HOSTNAME='my-custom-ip-address-or-hostname'
npm start

The above example would cause the development server to listen on exp://my-custom-ip-address-or-hostname:19000.

Sharing and Deployment

Expo does a lot of work to make app setup and development simple and straightforward. Using the managed workflow, Expo will even compile for the app stores. Expo's standalone builds tool will let you get an IPA/APK for distribution without having to build the native code yourself. If you need to switch to the bare workflow you are responsible for compiling and uploading to the app stores using local resources.

Publishing to Expo's React Native Community

Expo provides free hosting for the JS-only, allowing you to share your app through the Expo client app. This requires registration for an Expo account.

$ expo publish

Troubleshooting

Networking

If you're unable to load your app on your phone due to a network timeout or a refused connection, a good first step is to verify that your phone and computer are on the same network and that they can reach each other. Expo needs access to ports 19000 and 19001 so ensure that your network and firewall settings allow access from your device to your computer on both of these ports.

Try opening a web browser on your phone and opening the URL that the packager script prints, replacing exp:// with http://. So, for example, if underneath the QR code in your terminal you see:

exp://192.168.0.1:19000

Try opening Safari or Chrome on your phone and loading

http://192.168.0.1:19000

and

http://192.168.0.1:19001

If you're not able to load the http URL in your phone's web browser, try using the tethering/mobile hotspot feature on your phone (beware of data usage, though), connecting your computer to that WiFi network, and restarting the packager.

iOS Simulator won't open

If you're on a Mac, there are a few errors that users sometimes see when attempting to npm run ios:

• "non-zero exit code: 107"
• "You may need to install Xcode" but it is already installed
• and others

There are a few steps you may want to take to troubleshoot these kinds of errors:

1. Make sure Xcode is installed and open it to accept the license agreement if it prompts you. You can install it from the Mac App Store.
2. Open Xcode's Preferences, the Locations tab, and make sure that the Command Line Tools menu option is set to something. Sometimes when the CLI tools are first installed by Homebrew this option is left blank, which can prevent Apple utilities from finding the simulator. Make sure to re-run npm/yarn run ios after doing so.
3. If that doesn't work, open the Simulator, and under the app menu select Reset Contents and Settings.... After that has finished, quit the Simulator, and re-run npm/yarn run ios.

QR Code does not scan

If you're not able to scan the QR code, make sure your phone's camera is focusing correctly, and also make sure that the contrast on the two colors in your terminal is high enough. For example, WebStorm's default themes may not have enough contrast for terminal QR codes to be scannable with the system barcode scanners that the Expo app uses.

If this causes problems for you, you may want to try changing your terminal's color theme to have more contrast, or running Expo from a different terminal. You can also manually enter the URL printed by the packager script in the Expo app's search bar to load it manually.