Skip to main content

Debugging Basics

Accessing the Dev Menu​

React Native provides an in-app developer menu which offers several debugging options. You can access the Dev Menu by shaking your device or via keyboard shortcuts:

  • iOS Simulator: Cmd ⌘ + D (or Device > Shake)
  • Android emulators: Cmd ⌘ + M (macOS) or Ctrl + M (Windows and Linux)

Alternatively for Android devices and emulators, you can run adb shell input keyevent 82 in your terminal.

The React Native Dev Menu

note

The Dev Menu is disabled in release (production) builds.

Opening the Debugger​

The debugger allows you to understand and debug how your JavaScript code is running, similar to a web browser.

info

In Expo projects, press j in the CLI to directly open the Hermes Debugger.

Flipper is a native debugging tool which provides JavaScript debugging capabilities for React Native via an embedded Chrome DevTools panel.

To debug JavaScript code in Flipper, select "Open Debugger" from the Dev Menu. Learn more about Flipper here.

info

To debug using Flipper, the Flipper app must be installed on your system.

The Flipper desktop app opened to the Hermes debugger panel

warning

Debugging React Native apps with Flipper is deprecated in React Native 0.73. We will eventually remove out-of-the box support for JS debugging via Flipper.

React DevTools​

You can use React DevTools to inspect the React element tree, props, and state.

npx react-devtools

A React DevTools window

tip

Learn how to use React DevTools!

LogBox​

Errors and warnings in development builds are displayed in LogBox inside your app.

A LogBox warning and an expanded LogBox syntax error

note

LogBox is disabled in release (production) builds.

Console Errors and Warnings​

Console errors and warnings are displayed as on-screen notifications with a red or yellow badge, and a notification count. To see more about an error or warning, tap the notification to see an expanded view and to paginate through other logs.

LogBox notifications can be disabled using LogBox.ignoreAllLogs(). This can be useful when giving product demos, for example. Additionally, notifications can be disabled on a per-log basis via LogBox.ignoreLogs(). This can be useful for noisy warnings or those that cannot be fixed, e.g. in a third-party dependency.

info

Ignore logs as a last resort and create a task to fix any logs that are ignored.

import {LogBox} from 'react-native';

// Ignore log notification by message
LogBox.ignoreLogs([
  // Exact message
  'Warning: componentWillReceiveProps has been renamed',

  // Substring or regex match
  /GraphQL error: .*/,
]);

// Ignore all log notifications
LogBox.ignoreAllLogs();

Syntax Errors​

When a JavaScript syntax error occurs, LogBox will open with the location of the error. In this state, LogBox is not dismissable since your code cannot be executed. LogBox will automatically dismiss once the syntax error is fixed — either via Fast Refresh or after a manual reload.

Performance Monitor​

On Android and iOS, an in-app performance overlay can be toggled during development by selecting "Perf Monitor" in the Dev Menu. Learn more about this feature here.

The Performance Monitor overlay on iOS and Android

info

The Performance Monitor runs in-app and is a guide. We recommend investigating the native tooling under Android Studio and Xcode for accurate performance measurements.