react-native/docs/Debugging.md

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Debugging React Native Apps

To access the in-app developer menu:

1. On iOS shake the device or press control + ⌘ + z in the simulator.
2. On Android shake the device or press hardware menu button (available on older devices and in most of the emulators, e.g. in genymotion you can press ⌘ + m or F2 to simulate hardware menu button click). You can also install Frappé, a tool for OS X, which allows you to emulate shaking of devices remotely. You can use ⌘ + Shift + R as a shortcut to trigger a shake from Frappé.

Hint

To disable the developer menu for production builds:

1. For iOS open your project in Xcode and select Product → Scheme → Edit Scheme... (or press ⌘ + <). Next, select Run from the menu on the left and change the Build Configuration to Release.
2. For Android, by default, developer menu will be disabled in release builds done by gradle (e.g with gradle assembleRelease task). Although this behavior can be customized by passing proper value to ReactInstanceManager#setUseDeveloperSupport.

Android logging

Run adb logcat *:S ReactNative:V ReactNativeJS:V in a terminal to see your Android app's logs.

Reload

Selecting Reload (or pressing ⌘ + r in the iOS simulator) will reload the JavaScript that powers your application. If you have added new resources (such as an image to Images.xcassets on iOS or to res/drawable folder on Android) or modified any native code (Objective-C/Swift code on iOS or Java/C++ code on Android), you will need to re-build the app for the changes to take effect.

YellowBox/RedBox

Using console.warn will display an on-screen log on a yellow background. Click on this warning to show more information about it full screen and/or dismiss the warning.

You can use console.error to display a full screen error on a red background.

By default, the warning box is enabled in __DEV__. Set the following flag to disable it:

console.disableYellowBox = true;
console.warn('YellowBox is disabled.');

Specific warnings can be ignored programmatically by setting the array:

console.ignoredYellowBox = ['Warning: ...'];

Strings in console.ignoredYellowBox can be a prefix of the warning that should be ignored.

Chrome Developer Tools

To debug the JavaScript code in Chrome, select Debug JS Remotely from the developer menu. This will open a new tab at http://localhost:8081/debugger-ui.

In Chrome, press ⌘ + option + i or select View → Developer → Developer Tools to toggle the developer tools console. Enable Pause On Caught Exceptions for a better debugging experience.

To debug on a real device:

1. On iOS - open the file RCTWebSocketExecutor.m and change localhost to the IP address of your computer. Shake the device to open the development menu with the option to start debugging.
2. On Android, if you're running Android 5.0+ device connected via USB you can use adb command line tool to setup port forwarding from the device to your computer. For that run: adb reverse tcp:8081 tcp:8081 (see this link for help on adb command). Alternatively, you can open dev menu on the device and select Dev Settings, then update Debug server host for device setting to the IP address of your computer.

Custom JavaScript debugger

To use a custom JavaScript debugger define the REACT_DEBUGGER environment variable to a command that will start your custom debugger. That variable will be read from the Packager process. If that environment variable is set, selecting Debug JS Remotely from the developer menu will execute that command instead of opening Chrome. The exact command to be executed is the contents of the REACT_DEBUGGER environment variable followed by the space separated paths of all project roots (e.g. 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 end up being executed). Custom debugger commands executed this way should be short-lived processes, and they shouldn't produce more than 200 kilobytes of output.

Live Reload

This option allows for your JS changes to trigger automatic reload on the connected device/emulator. To enable this option:

1. On iOS, select Enable Live Reload via the developer menu to have the application automatically reload when changes are made to the JavaScript.
2. On Android, launch dev menu, go to Dev Settings and select Auto reload on JS change option

FPS (Frames per Second) Monitor

On 0.5.0-rc and higher versions, you can enable a FPS graph overlay in the developers menu in order to help you debug performance problems.