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Version: v11.12.1

React Native DevTools

React Native DevTools is the new debugging tool for Expo and React Native apps (since version 0.76), replacing Chrome DevTools. This guide explains how to use it to check re-renders and analyze performance, especially for WaveMaker apps.

Generally, too many re-renders can slow down React Native apps. React Native DevTools can highlight component re-renders as they happen, helping you identify unnecessary updates and optimize your application's performance on mobile devices.

React Native DevTools provides access to console, sources, memory, components, and profiler tabs, with built-in support for React DevTools functionality.

Prerequisites​

Before you begin, ensure you have the proper setup:

  1. React Native 0.76 or later (React Native DevTools replaces Chrome DevTools)
  2. Development mode - Ensure your React Native app is running in development mode

Opening React Native DevTools​

To open React Native DevTools:

  1. Start your app with Expo CLI or React Native CLI
  2. Press j in the terminal where Expo or React Native starts
  3. React Native DevTools will open in a separate window automatically

For detailed setup instructions, refer to the official Expo debugging documentation.

Debugging React Components​

Components Tab​

The Components tab shows the structure of your React Native app. It lets you see all components in a tree-like view, check their props and state, and watch how they update in real time when the app re-renders.

Accessing Component Tab​

There are two main approaches depending on your React Native version and setup:

Option 1: React Native DevTools (React Native 0.76+)​

For React Native 0.76 and later versions, React Native DevTools includes built-in React DevTools functionality:

  1. Open React Native DevTools by pressing j in your terminal where you started your development server
  2. Navigate to the Components tab (one of the available tabs alongside console, sources, network, memory, and profiler)
  3. The component tree will display your React Native app's component hierarchy with built-in React DevTools features

Option 2: Standalone React DevTools (All React Native versions)​

For older React Native versions or when you prefer using standalone React DevTools:

  1. Install react-devtools globally:

    npm install -g react-devtools

  2. Start react-devtools in a separate terminal:

    npx react-devtools

  3. Connect your app to react-devtools:

    • For Expo: React DevTools should connect automatically when you start your app
    • For React Native CLI: Ensure your app is running in development mode and react-devtools will connect automatically

  4. The React DevTools window will open with the Components and Profiler tabs available

Enabling Highlight Updates​

To visualize component re-renders:

  1. In the Components tab, click the settings gear icon in the top right corner
  2. Enable "Highlight Updates" from the settings menu
  3. Interact with your app to see components flash with colored borders as they re-render

Understanding Update Highlights​

Once enabled, interact with your React Native app to see components flash with colored borders as they re-render:

  • Blue: Infrequent updates - Generally acceptable
  • Green: Moderate updates - Monitor for optimization opportunities
  • Yellow: Frequent updates - Potential performance concern
  • Red: Very frequent updates - Requires immediate attention

Inspecting React Native Components​

  • Click on Components in the component tree to examine their props and state
  • Look for unexpected re-renders in native components (View, Text, ScrollView, etc.)
  • Identify React Native-specific performance bottlenecks like unnecessary bridge communications
  • Use the search functionality to quickly find specific components in large component trees

Profiler Tab: Deep Performance Analysis​

The Profiler tab provides detailed performance metrics specifically tailored for React Native applications using the built-in React DevTools profiler functionality.

Recording a Profiling Session​

Follow these steps to record and analyze a profiling session in React Native:

  1. Navigate to the Profiler tab in React Native DevTools
  2. Click the Record button (circular record icon) to start profiling
  3. Interact with your React Native app to trigger the behavior you want to analyze
  4. Click Stop to end the recording session and view the profiling results

Understanding React Native Profiler Data​

The Profiler provides several views and metrics optimized for React Native:

Flamegraph View​

  • Visual representation of React Native component render times
  • Wider bars indicate longer render times
  • Color coding shows performance relative to other React Native components
  • Identifies bridge communication bottlenecks

Ranked View​

  • Lists React Native components ordered by render time
  • Identifies the slowest native and JavaScript components for optimization
  • Shows actual vs. base render times for React Native elements

Component Chart​

  • Timeline view of individual React Native component renders
  • Shows when components rendered during the session
  • Helps identify render frequency patterns specific to mobile interactions
note

In the above example, you can see that the View rendered 4 times during the profiling session and was expensive, indicating a potential performance optimization opportunity.

Key Metrics for React Native​

  • Render Duration: Time taken to render each React Native component
  • Commit Duration: Time taken to apply changes to the native UI
  • Self Time: Time spent in the component itself (excluding children)
  • Total Time: Time including all child components

Debugging Common React Native Performance Issues​

Identifying Unnecessary Re-renders in React Native​

Look for these patterns specific to React Native applications:

  1. Native components rendering without prop changes
  2. Frequent renders of expensive native components (like FlatList, Image)
  3. Deep React Native component trees re-rendering together
  4. Components with consistent high render times affecting UI thread performance

Recording Why React Native Components Rendered​

To understand why React Native components are re-rendering:

  1. Enable Record why each component rendered while profiling in React Native DevTools settings

  2. Record a new profiling session
  3. Select a React Native component in the profiler
  4. View the What caused this update? information panel

This feature shows:

  • Props changes that triggered the re-render in React Native components
  • State changes within React Native components
  • Parent component re-renders that caused cascading updates in the native UI

Debugging Tips: Using React Native DevTools with Different Setups​

Expo Development Build​

For Expo apps using development builds:

  1. Start your Expo development build:

    npx expo run:android
    # or
    npx expo run:ios

  2. Press j in the terminal to open React Native DevTools

Expo Go​

When using Expo Go:

  1. Start your project:

    npx expo start

  2. Press j in the terminal to open React Native DevTools

Standard React Native CLI Projects​

For React Native CLI projects (React Native 0.76+):

  1. Start your development server:

    npx react-native start

  2. Run your app:

    npx react-native run-android
    # or
    npx react-native run-ios

  3. Press j in the terminal to open React Native DevTools

Production Profiling​

For production performance analysis:

Expo Projects​

Create a production build:

npx expo run:android --variant release

References​