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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 to simulate hardware menu button click)

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.

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.

Chrome Developer Tools

To debug the JavaScript code in Chrome, select Debug in Chrome 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 8081 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.

React Developer Tools (optional)

Install the React Developer Tools extension for Google Chrome. This will allow you to navigate the component hierarchy via the React in the developer tools (see facebook/react-devtools for more information).

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.