Enabling Keyboard Shortcuts
React Native supports a few keyboard shortcuts in the iOS Simulator. They are described below. To enable them, open the Hardware menu, select Keyboard, and make sure that "Connect Hardware Keyboard" is checked.
Accessing the In-App Developer Menu
You can access the developer menu by shaking your device or by selecting "Shake Gesture" inside the Hardware menu in the iOS Simulator. You can also use the
⌘D keyboard shortcut when your app is running in the iOS Simulator, or
⌘M when running in an Android emulator on Mac OS and
Ctrl+M on Windows and Linux. Alternatively for Android, you can run the command
adb shell input keyevent 82 to open the dev menu (82 being the Menu key code).
The Developer Menu is disabled in release (production) builds.
⌘R in the iOS Simulator, or tap
R twice on Android emulators.
You can speed up your development times by having your app reload automatically any time your code changes. Automatic reloading can be enabled by selecting "Enable Live Reload" from the Developer Menu.
There are some instances where hot reloading cannot be implemented perfectly. If you run into any issues, use a full reload to reset your app.
You will need to rebuild your app for changes to take effect in certain situations:
- You have added new resources to your native app's bundle, such as an image in
Images.xcassetson iOS or the
res/drawablefolder on Android.
- You have modified native code (Objective-C/Swift on iOS or Java/C++ on Android).
In-app Errors and Warnings
Errors and warnings are displayed inside your app in development builds.
In-app errors are displayed in a full screen alert with a red background inside your app. This screen is known as a RedBox. You can use
console.error() to manually trigger one.
Warnings will be displayed on screen with a yellow background. These alerts are known as YellowBoxes. Click on the alerts to show more information or to dismiss them.
As with a RedBox, you can use
console.warn() to trigger a YellowBox.
YellowBoxes can be disabled during development by using
console.disableYellowBox = true;. Specific warnings can be ignored programmatically by setting an array of prefixes that should be ignored:
In CI/Xcode, YellowBoxes can also be disabled by setting the
IS_TESTING environment variable.
RedBoxes and YellowBoxes are automatically disabled in release (production) builds.
Chrome Developer Tools
Tools → Developer Tools from the Chrome Menu to open the Developer Tools. You may also access the DevTools using keyboard shortcuts (
⌘⌥I on macOS,
I on Windows). You may also want to enable Pause On Caught Exceptions for a better debugging experience.
Note: the React Developer Tools Chrome extension does not work with React Native, but you can use its standalone version instead. Read this section to learn how.
REACT_DEBUGGER environment variable to a command that will start your custom debugger. You can then select "Debug JS Remotely" from the Developer Menu to start debugging.
The debugger will receive a list of all project roots, separated by a space. For example, if you set
REACT_DEBUGGER="node /path/to/launchDebugger.js --port 2345 --type ReactNative", then the command
node /path/to/launchDebugger.js --port 2345 --type ReactNative /path/to/reactNative/app will be used to start your debugger.
Custom debugger commands executed this way should be short-lived processes, and they shouldn't produce more than 200 kilobytes of output.
Safari Developer Tools
You can use Safari to debug the iOS version of your app without having to enable "Debug JS Remotely".
- Enable Develop menu in Safari:
Preferences → Advanced → Select "Show Develop menu in menu bar"
- Select your app's JSContext:
Develop → Simulator → JSContext
- Safari's Web Inspector should open which has a Console and a Debugger
However, there are some disadvantages:
- No sourcemaps when debugging
- Every time the app is reloaded (using live reload, or by manually reloading), a new JSContext is created. Choosing "Automatically Show Web Inspectors for JSContexts" saves you from having to select the latest JSContext manually.
React Developer Tools
You can use the standalone version of React Developer Tools to debug the React component hierarchy. To use it, install the
react-devtools package globally:
react-devtools from the terminal to launch the standalone DevTools app:
It should connect to your simulator within a few seconds.
Note: if you prefer to avoid global installations, you can add
react-devtoolsas a project dependency. Add the
react-devtoolspackage to your project using
npm install --save-dev react-devtools, then add
"react-devtools": "react-devtools"to the
scriptssection in your
package.json, and then run
npm run react-devtoolsfrom your project folder to open the DevTools.
Integration with React Native Inspector
Open the in-app developer menu and choose "Toggle Inspector". It will bring up an overlay that lets you tap on any UI element and see information about it:
react-devtools is running, Inspector will enter a collapsed mode, and instead use the DevTools as primary UI. In this mode, clicking on something in the simulator will bring up the relevant components in the DevTools:
You can choose "Toggle Inspector" in the same menu to exit this mode.
Inspecting Component Instances
First, follow the instructions for debugging in Chrome to open the Chrome console.
Make sure that the dropdown in the top left corner of the Chrome console says
debuggerWorker.js. This step is essential.
Then select a React component in React DevTools. There is a search box at the top that helps you find one by name. As soon as you select it, it will be available as
$r in the Chrome console, letting you inspect its props, state, and instance properties.
You can enable a performance overlay to help you debug performance problems by selecting "Perf Monitor" in the Developer Menu.
Accessing console logs
You can display the console logs for an iOS or Android app by using the following commands in a terminal while the app is running:
You may also access these through
Debug → Open System Log... in the iOS Simulator or by running
adb logcat *:S ReactNative:V ReactNativeJS:V in a terminal while an Android app is running on a device or emulator.
If you're using Create React Native App or Expo CLI, console logs already appear in the same terminal output as the bundler.
Debugging on a device with Chrome Developer Tools
If you're using Create React Native App or Expo CLI, this is configured for you already.
On iOS devices, open the file
RCTWebSocketExecutor.m and change "localhost" to the IP address of your computer, then select "Debug JS Remotely" from the Developer Menu.
On Android 5.0+ devices connected via USB, you can use the
adb command line tool to setup port forwarding from the device to your computer:
adb reverse tcp:8081 tcp:8081
Alternatively, select "Dev Settings" from the Developer Menu, then update the "Debug server host for device" setting to match the IP address of your computer.
If you run into any issues, it may be possible that one of your Chrome extensions is interacting in unexpected ways with the debugger. Try disabling all of your extensions and re-enabling them one-by-one until you find the problematic extension.
Debugging native code
When working with native code, such as when writing native modules, you can launch the app from Android Studio or Xcode and take advantage of the native debugging features (setting up breakpoints, etc.) as you would in case of building a standard native app.