Error Boundaries

Catching errors, fallback UIs, error reporting, and graceful degradation.

Overview

Error boundaries catch JavaScript errors in their child component tree and display fallback UI.

Key Concepts

• componentDidCatch — Catches errors during rendering
• getDerivedStateFromError — Updates state when error occurs
• Fallback UI — User-friendly error display
• Error Reporting — Log errors to monitoring services
• Granular Boundaries — Wrap specific sections, not entire app

Code Examples

import { Component } from 'react';

class ErrorBoundary extends Component {
  constructor(props) {
    super(props);
    this.state = { hasError: false, error: null };
  }

  static getDerivedStateFromError(error) {
    return { hasError: true, error };
  }

  componentDidCatch(error, errorInfo) {
    console.error('Error caught:', error, errorInfo);
    // Send to error reporting service
  }

  render() {
    if (this.state.hasError) {
      return (
        <div className="error-fallback">
          <h2>Something went wrong</h2>
          <p>{this.state.error?.message}</p>
          <button onClick={() => this.setState({ hasError: false })}>
            Try again
          </button>
        </div>
      );
    }
    return this.props.children;
  }
}

// Usage
function App() {
  return (
    <ErrorBoundary>
      <Header />
      <main>
        <ErrorBoundary>
          <Sidebar />
        </ErrorBoundary>
        <Content />
      </main>
    </ErrorBoundary>
  );
}

Practice

Create an error boundary that logs errors and provides a retry mechanism.