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Expo

Blog:

VSCode plugin 'Expo Tools': https://marketplace.visualstudio.com/items?itemName=expo.vscode-expo-tools

tip

Run npx expo-doctor@latest to validate various things like dependency

Keyboard shortcuts​

After doing npx expo start, you can use the keys (r, i, a...) listed table at https://docs.expo.dev/more/expo-cli/#develop

Show developer menu​

https://docs.expo.dev/debugging/tools/#developer-menu

  • Android device or emulator
    • Press Cmd/Ctrl + M
    • Shake your device ????
    • Run adb shell input keyevent 82 or adb shell input keyevent KEYCODE_MENU ???
  • iOS simulator
    • Cmd + D
    • Cmd + Ctrl + Z (shake your device). You can also do Device → Shake

app.json / app.config.js / app.config.ts​

Configuration with app.json / app.config.js: https://docs.expo.dev/workflow/configuration/

Properties: https://docs.expo.dev/versions/latest/config/app/

View the resulting app.config.ts configuration:

npx expo config
npx expo config --full
npx expo config --type public
npx expo config --type prebuild
npx expo config --type introspect

See the docs for more info on config types: https://docs.expo.dev/more/expo-cli/#config

infoPlist​

https://docs.expo.dev/versions/latest/config/app/#infoplist

Info.plist can also be modified with a config plugin: https://docs.expo.dev/guides/config-plugins/#modifying-the-infoplist

Examples: https://github.com/search?q=%22infoPlist%22+extension%3Ajson+path%3A%2F+filename%3Aapp.json&type=Code&ref=advsearch&l=&l=

{
  "expo": {
    "ios": {
      "infoPlist": {
        "LSApplicationQueriesSchemes": ["comgooglemaps"],
        "NSCameraUsageDescription": "This app uses the camera to scan barcodes on event tickets.",
        "CFBundleAllowMixedLocalizations": true,
        "ITSAppUsesNonExemptEncryption": false
      }
    }
  }
}

CLI​

Docs: https://docs.expo.dev/more/expo-cli

List commands: npx expo --help or npx expo -h

Highlights​

From https://docs.expo.dev/more/expo-cli/#highlights

  • Start a server for developing your app: npx expo start.
  • Generate the native Android and iOS directories for your project: npx expo prebuild. See the Prebuild documentation for more. Tip: use --clean to delete any existing native directories before generating.
  • Build and run the native apps locally: npx expo run:ios and npx expo run:android.
    • Important: expo run also generates the native projects if they don't exist yet: if your project does not have an ios directory in the root of your project, then npx expo run:ios will first run npx expo prebuild -p ios before compiling your app
  • Install and update packages that work with the version of react-native in your project: npx expo install package-name.
  • npx expo can be used with npx react-native simultaneously.

Local CLI (introduced in SDK 46)​

SDK 46 (released August 2022) removes the global npm install expo-cli.

The New Expo CLI (2022-08) - https://blog.expo.dev/the-new-expo-cli-f4250d8e3421

  • A new “Local Expo CLI” replaces the “Global Expo CLI”
  • In the new Local Expo CLI, expo eject is no longer available, it’s been fully replaced by npx expo prebuild

Beta: Local Expo CLI (2022-04) - https://blog.expo.dev/new-versioned-expo-cli-cf6e10632656

Use expo install instead of yarn add/npm install because it picks the library versions compatible with the Expo SDK​

See https://docs.expo.dev/bare/using-expo-client/#prefer--expo-install--over-

Prefer expo install over npm install to add Expo SDK packages This will ensure that you get a version of the package that is compatible with the SDK version in your app. If you use npm install directly instead, you may end up with a newer version of the package that isn't supported in Expo Go yet.

This is also explained at https://reactnavigation.org/docs/getting-started#installing-dependencies-into-an-expo-managed-project

Create new app/project​

See https://docs.expo.dev/get-started/create-a-project/

npx create-expo-app my-app
npx create-expo-app --template expo-template-blank-typescript

Available templates: https://github.com/expo/expo/tree/main/templates

Use TypeScript: https://docs.expo.dev/guides/typescript/

Old, using `expo init`
expo init <appname> --yarn
expo init <appname> -t expo-template-blank-typescript
expo init --template bare-minimum # warning: does not add react-navigation!

See expo init options at https://docs.expo.dev/workflow/expo-cli/#expo-init

Note that option --name is deprecated, if you use it says "Use expo init [name] instead of --name [name]".

Validate package versions compatibility and install compatible versions​

Important: you can also use npx expo-doctor@latest which runs many other checks.

Docs: https://docs.expo.dev/more/expo-cli/#install

npx expo install --check # Check which installed packages need to be updated
npx expo install --fix # Automatically update any invalid package versions

You can check/fix specific packages, eg npx expo install expo-camera --check.

Eg doing npx expo install --check will output:

Some dependencies are incompatible with the installed expo version:
  @react-native-community/slider@4.4.3 - expected version: 4.4.2
Your project may not work correctly until you install the correct versions of the packages.
Install individual packages by running npx expo install @react-native-community/slider@4.4.2
✔ Fix dependencies? (Y/n)

Shift+i allows you to choose in which simulator to run the app on​

Source: https://github.com/expo/expo-cli/issues/2413#issuecomment-969098866

Expo Dev Client / Development builds / Custom Development Clients​

Docs: https://docs.expo.dev/develop/development-builds/introduction

Replaces Expo Go, which contains a fixed collection of native modules and does not allow custom native code.

Expo Go is not recommended for building production-quality apps — use development builds instead. source

When your project requires custom native code, a config plugin, a custom runtime version, or a reduced bundle size of the app, you can transition from using Expo Go to developing a development build. source

It’s a React Native library that gives you the same experience as Expo Go, but with your own custom runtime. source

What's an Expo Development Build? - https://www.youtube.com/watch?v=Iw8FAUftJFU

https://www.npmjs.com/package/expo-dev-client

https://docs.expo.dev/development/introduction (old, redirects to https://docs.expo.dev/develop/development-builds/introduction/)

Expo Go app is a standard client containing a preset collection of modules. As your project moves toward release, you may find that you need to customize your project, either to reduce your bundle size, to use a module offered by developers in the React Native community, or even to add your own custom native code.

You can think of a development build as your fully customizable version of Expo Go.

https://blog.expo.dev/introducing-custom-development-clients-5a2c79a9ddf8

(managed workflow) If you add or change the version of any modules in your project that includes native code or make most changes to your app.json, you’ll need to generate a new custom client to be able to run your app.

More information:

Type of builds​

From https://docs.expo.dev/develop/development-builds/introduction/

A development build of your app is a Debug build that contains the expo-dev-client package. As a production build is for the general public, and a preview build lets your team test your next release, a development build lets developers iterate as quickly as possible. It comes with extensible development tools to develop and test your project.

https://docs.expo.dev/build/eas-json/#development-builds

These builds include developer tools, and they are never submitted to an app store.

  • Development
  • Preview
    • https://docs.expo.dev/build/eas-json/#preview-builds
    • For internal testing
    • Doesn't include developer tools
    • They are either not signed for distribution on stores (ad hoc or enterprise provisioning on iOS), or are packaged in a way that is not optimal for store deployment (Android APK is best for preview, AAB is best for stores)
  • Production
    • https://docs.expo.dev/build/eas-json/#production-builds
    • For the general public
    • Submitted to the store
    • Production builds must be installed through their respective app stores. They cannot be installed directly on your Android Emulator or device, or iOS Simulator or device. The only exception to this is if you explicitly set "buildType": "apk" for Android on your build profile. However, it is recommended to use aab when submitting to stores, and this is the default configuration. source

expo-dev-client setup / create a development build​

Follow https://docs.expo.dev/develop/development-builds/create-a-build/ (old URL: https://docs.expo.dev/development/getting-started/)

You need to have "developmentClient": true on eas.json:

eas.json
{
  "build": {
    "development": {
      "developmentClient": true,
      "distribution": "internal"
    }
  }
}

This creates a 'Development build', a Debug build of your project that includes the expo-dev-client. See https://docs.expo.dev/development/getting-started/ and https://docs.expo.dev/development/build/.

To install run expo install expo-dev-client, then npx pod-install.

To create a development build do:

eas build -p ios --profile development
eas build -p android --profile development

After the build is created, install it on your device. Afterwards, to run the app do expo start --dev-client and click 'i' or 'a', or scan the QR code.

Now you won't have to wait for the native build process again until you change the underlying native code that powers your app.

Config Plugins​

https://docs.expo.dev/config-plugins/introduction/

When you add a native library (npx expo install expo-camera), you'll also add a plugin at the app.json / app.config.js / app.config.ts file:

app.config.ts
{
  plugins: [
    'expo-camera', // https://docs.expo.dev/versions/latest/sdk/camera/
    'expo-build-properties', // https://docs.expo.dev/versions/latest/sdk/build-properties/
    'react-native-health', // From https://www.youtube.com/watch?v=Iw8FAUftJFU&t=182s
    './config-plugins/my-xyz-plugin',
  ]
}

In addition to expo eject, now there is also expo prebuild​

See the 2 images in https://blog.expo.dev/expo-managed-workflow-in-2021-d1c9b68aa10

Now to get our managed project into a state where we can build it on EAS Build, we can repurpose the “eject” command to generate and configure the native iOS and Android projects based on the JavaScript app. We call this new command “prebuild”.

Info about prebuild: https://github.com/expo/fyi/blob/main/prebuilding.md

you might need to use a library that doesn't have a config plugin yet, or maybe you need to write some custom native code yourself. For these cases you'll have to manually modify the ios and android folders, doing this means you'll no longer be able to safely rerun expo prebuild.

Eject moves from manged to bare, and it's run once ever.

expo prebuild is very similar to expo eject, the core difference being that eject is intended to be run once, and prebuild can be used multiple times. The eject command assumes that your ios and android folders are modified by hand (bare workflow) and will warn you if they might be overwritten, whereas the prebuild command should only be used when your ios and android folders are completely generated and can be regenerated any time (kinda like the node_modules folder).

More info about prebuild in 'Adding custom native code': https://docs.expo.dev/workflow/customizing/

EAS​

Expo Application Services. A cloud build service capable of building projects with arbitrary native code.

https://blog.expo.dev/introducing-eas-395d4809cc6f

https://expo.dev/eas

https://docs.expo.dev/eas

https://blog.expo.dev/expo-application-services-eas-build-and-submit-fc1d1476aa2e

Install the CLI: npm install -g eas-cli (npm is recommended instead of yarn)

Login: eas login

Check the current user: eas whoami

eas.json​

Properties:

EAS Build​

Replaces expo build:ios and expo build:android (classic build, which uses a 'shell app').

Docs: https://docs.expo.dev/build/introduction

expo build’s Final Year: https://blog.expo.dev/turtle-goes-out-to-sea-d334db2a6b60

https://blog.expo.dev/expo-managed-workflow-in-2021-5b887bbf7dbb (part 1)

https://blog.expo.dev/expo-managed-workflow-in-2021-d1c9b68aa10 (part 2)

eas build:configure → Generates eas.json. Learn more at https://docs.expo.dev/build-reference/build-configuration/

To install an app to an iPhone, first register the device UDID at https://developer.apple.com/account/resources/devices/list. To register any iOS devices you would like to develop on to your ad hoc provisioning profile use eas device:create.

Android build:

iOS build:

Android and iOS build: eas build -p all

Build locally (eg to generate an aab file to upload to Google Play):

Download a simulator build from EAS servers and run it directly on your emulator/simulator in a snap:

tip

Attach a message to distinguish builds with eas build --platform ios --message "JIRA-XYZ PR #650"

You can attach a message to the build by passing --message to the build command. The message will appear on the website. It comes in handy when you want to leave a note with the purpose of the build for your team. source

Troubleshoot EAS builds​

If you get an error when doing eas build see this: https://docs.expo.dev/build-reference/local-builds/#use-local-builds-for-debugging

It's helpful to run the build locally with --local, and to use EAS_LOCAL_BUILD_SKIP_CLEANUP=1 to see the generated android and ios folders which disables cleaning up the working directory after the build process is finished:

EAS_LOCAL_BUILD_SKIP_CLEANUP=1 eas build --platform android --profile testing --local

It will output the folder at the end, even if the build fails:

Skipping cleanup, /var/folders/wz/fw48m6mx50b_hy2w3kj4lvl40000gn/T/eas-build-local-nodejs/9f6700b0-e08a-45c9-a906-a9260b118f43 won't be removed.

Also see https://github.com/expo/eas-build/blob/main/DEVELOPMENT.md

Signing​

https://docs.expo.dev/app-signing/app-credentials/

Use eas credentials to manage (create, download, delete) Android keystores, iOS distribution certificates etc.

Signing Android​

https://docs.expo.dev/app-signing/app-credentials/#app-signing-by-google-play

From the Expo build process's perspective, there is no difference whether an app is signed with an upload certificate or an app signing key. Either way, eas build will generate an APK or AAB signed with the keystore currently associated with your application. If you want to generate an upload keystore manually, you can do that the same way you created your original keystore.

EAS Submit​

App store submissions.

The very first Android build must be uploaded manually to Google Play - see https://docs.expo.dev/submit/android/#manually-uploading-your-app-for-the-first. This is not required on App Store (iOS).

After building with eas build we can do eas submit -p ios to publish to the App Store. There is also the option --auto-submit, so we can do both build and submit, eg: eas build -p ios --profile production --auto-submit.

To publish to Google Play we need the service account key, which gives API access: https://github.com/expo/fyi/blob/main/creating-google-service-account.md. Note that the API access menu item appears at the main Google Play console page, not the app-specific page.

EAS Update​

https://docs.expo.dev/eas-update/introduction

https://blog.expo.dev/eas-update-in-preview-d221b6f91f52

Deliver small updates of the non-native parts of your app (JS, styling, image assets...) to your users in between build and submit cycles

https://blog.expo.dev/eas-update-preview-progress-f504a30066fc

EAS Update also doubles as a workflow efficiency tool, streamlining feedback loops by allowing teams to share previews of their projects during PR review. We love being able to push to GitHub, trigger a GitHub action to publish an update, then see it immediately inside of a development build.

Using Expo OTA Updates in your React Native app - Eric Samelson at @ReactEurope 2020: https://www.youtube.com/watch?v=Si909la3rLk

Gotcha from https://docs.expo.dev/eas-update/environment-variables/

When you run eas update, any .env files present will be evaluated when your JavaScript is bundled. Any EXPO_PUBLIC variables in your application code will be replaced inline with the corresponding values from your .env files that are present on the machine from which the update is published, whether that is your local machine or your CI/ CD server.

Run the production app​

See https://docs.expo.dev/workflow/development-mode/. There is also a switch in http://localhost:19002/.

expo start --no-dev --minify
# or if we've done a prebuild
expo start --no-dev --minify --dev-client

Environment variables and configuration​

Configuration with app.json / app.config.js: https://docs.expo.dev/workflow/configuration/

Environment variables in Expo: https://docs.expo.dev/guides/environment-variables/

Environment variables and secrets: https://docs.expo.dev/build-reference/variables/

Also see https://docs.expo.dev/build/eas-json/#environment-variables

For eas build, doing ENVIRONMENT=prod eas build does not work, ENVIRONMENT needs to be defined in eas.json. However, it works for "other commands that run entirely locally" like eas update. See https://github.com/expo/fyi/blob/main/eas-config-mismatch.md

According to https://docs.expo.dev/build-reference/variables/#can-i-share-environment-variables-defined-in expo start does not pick variables defined in eas.json:

When you define environment variables on build profiles in eas.json, they will not be available for local development when you run expo start (and expo publish).

SDK Versions/Releases​

https://docs.expo.dev/workflow/upgrading-expo-sdk-walkthrough/

CHANGELOG

Unimodules → Expo modules​

https://blog.expo.dev/whats-new-in-expo-modules-infrastructure-7a7cdda81ebc

https://github.com/expo/fyi/blob/main/expo-modules-migration.md

Using Expo modules in a standard React Native app (created with npx react-native init): https://docs.expo.dev/bare/installing-expo-modules

For module authors: https://blog.expo.dev/a-peek-into-the-upcoming-sweet-expo-module-api-6de6b9aca492

Expo (Native) Modules API​

https://docs.expo.dev/modules/overview/

https://twitter.com/tsapeta/status/1590353202402115584

Flipper​

https://twitter.com/Baconbrix/status/1412921581542658049

https://blog.expo.dev/expo-dev-client-0-8-0-7116c1945253

With plugin: