React Native

Setup

Official doc : https://reactnative.dev/docs/environment-setup (opens in a new tab)
Mac M1 might need

"EXCLUDED_ARCHS[sdk=iphonesimulator*]" = arm64;

Architecture

React Native apps have an entry point like a client side React app.

import { Text, AppRegistry } from 'react-native'
 
const App = (props) => (
  <View>
    <Text>App1</Text>
  </View>
)
 
AppRegistry.registerComponent('Appname', () => App)

Compared to React, React Native doesn't use react-dom (ex: <div/> jsx) but instead uses base components like View and Text to build the UI.

Metro

https://facebook.github.io/metro/docs/api (opens in a new tab)

Metro is a bundler (like Webpack/Vite) for React Native built by facebook. It turns the JS code into a single file.
yarn start runs a local server (like webpack dev server). It can the communicate with multiple devices/simulators.
yarn start --reset-cache to clear cache.
Metro does not support tree shaking. Make sure to remove unused code (eslint rules can help).

Bridge

The "Old Architecture" uses a bridge to communicate between the native thread and JS thread. It marshalls JSON messages which can have a performance cost.

New Architecture

Fabric

New rendering system. No bridge. Instead uses JSI (JavaScript Interface) to communicate directly with native code (C++ and JS).
3 phases :

• render: JS executes JSX instructions, that generates a JS tree, from which a C++ tree is created (shadow tree).
• commit: promotes the tree as "next to be mounted"
• mount: mounts the host view tree (uses Yoga https://yogalayout.com/ (opens in a new tab) to calculate the layout from 'CSS like' properties)

Hermes

A Javascript engine (like Node, ex: node test.js => hermes test.js). Optimized for React Native. https://hermesengine.dev/ (opens in a new tab)
Compiles JS to bytecode executable by Hermes. Ex: hermes -emit-binary -out test.hbc test.js && hermes test.hbc

Debugging

React Native Debugger (easy to get started): https://github.com/jhen0409/react-native-debugger (opens in a new tab)

Flipper (facebook's debugger): https://fbflipper.com/docs/features/react-native/ (opens in a new tab)

Popular Libraries

Animations:

React Native's Animated API (to get started)

Reanimated: https://docs.swmansion.com/react-native-reanimated/docs (opens in a new tab)

Gesture Handler: https://docs.swmansion.com/react-native-gesture-handler/docs/ (opens in a new tab)

Components:

Native Base 3: https://docs.nativebase.io/ (opens in a new tab) Mostly for prop based Layout Components (like Chakra UI) and building a design-systems on top of good a11y defaults. Can have performance issues.
@shopify/restyle is likely a better alternative.

Navigation:

React Navigation: https://reactnavigation.org/docs/getting-started (opens in a new tab)

dependencies:

https://microsoft.github.io/rnx-kit/docs/tools/dep-check (opens in a new tab)

Can check which dependencies are used in the project and if they fit together or have known issues.

yarn rnx-dep-check --vigilant 0.68.0

IOS

Cocoa Pods

https://cocoapods.org/ (opens in a new tab)

IOS's dependency management system (like npm or yarn).

Similar to npm install, pod install installs all dependencies.

Typically used together with npm/yarn whenever dependencies need to be updated.

npm install && cd ios && pod install && cd ..

Sometimes like rm -rf node_modules we can do:

cd ios && pod deintegrate && pod install && cd ..

Simulator

Keyboard shortcuts

R => reloads app D => opens debug menu I => inspect cmd+K => toggle keyboard (check layout)

Select device

xcrun simctl list devices # lists devices
npx react-native run-ios --simulator="iPhone 13 mini"

Android

Gradle

Versioning & java/kotlin build tool. Replaces Maven.

Jetifier

The "android" namespace was renamed "androidX", jetifier helps with retro compatibility with old libraries.

Physical device debugging

Upload APK to device

adb install ~/Downloads/build/app-release.apk

Check if device is connected

adb devices

Reconnect metro to physical device

adb reverse tcp:8081 tcp:8081
# then hit R to reload Metro

Retrieve logs

adb logcat -d > log.txt

Deploy

Bitrise: easy CI/CD pipelines

AppCenter: easy CI/CD pipelines

Differences between React (Web) and React Native

Shadows

Shadows have a different "CSS" API and platform specific:

shadowColor works on both ios and android.
On android, elevation is used to create shadows. (no effect on ios)
On IOS, shadowOffset, shadowOpacity and shadowRadius are used to create shadows. (no effect on android)

style={{
  shadowColor: "#000",
  shadowOffset: {
    width: 0,
  	height: 1,
  },
  shadowOpacity: 0.22,
  shadowRadius: 2.22,
 
  elevation: 3
}}

https://github.com/alan-eu/react-native-fast-shadow (opens in a new tab) offers a cross platform solution.

Animations & Gestures

Reanimated 2 & Gesture Handler are the main libraries.

Reanimated 2

Shared Values are computed on the UI thread, manipulated synchronously there, and read asynchronously on the RN JS thread.