23Error Boundaries and Handling Errors

Advanced22m

Why Errors Happen in React

React apps can break due to undefined variables, bad API responses, or unexpected bugs. Without error handling, a small bug in one component can crash your entire app.

What Is an Error Boundary?

An Error Boundary is a special React component that catches runtime errors in its child components during rendering and replaces the broken UI with a fallback instead of crashing the whole app.

Prevents full app crashes
Displays fallback UIs
Logs errors for debugging
Improves user experience

💡 Error Boundaries catch rendering errors, but not errors in async code or event handlers.

Creating a Basic Error Boundary

jsx

import React, { Component } from 'react'

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

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

  componentDidCatch(error, info) {
    console.error('Error caught by Error Boundary:', error, info)
  }

  render() {
    if (this.state.hasError) {
      return <h2>Something went wrong.</h2>
    }
    return this.props.children
  }
}

export default ErrorBoundary

Using an Error Boundary

jsx

import ErrorBoundary from './ErrorBoundary'
import Profile from './Profile'

export default function App() {
  return (
    <ErrorBoundary>
      <Profile />
    </ErrorBoundary>
  )
}

Custom Fallback UI

jsx

class ErrorBoundary extends Component {
  ...
  render() {
    if (this.state.hasError) {
      return (
        <div>
          <h2>Oops! Something broke.</h2>
          <button onClick={() => window.location.reload()}>Reload</button>
        </div>
      )
    }
    return this.props.children
  }
}

Handling Errors in Event Handlers

Error Boundaries do not catch errors inside event handlers. Use try/catch manually:

jsx

function handleClick() {
  try {
    throw new Error('Button failed!')
  } catch (error) {
    console.error(error)
  }
}

<button onClick={handleClick}>Click me</button>

Handling Async Errors

Async errors are not caught by Error Boundaries, so you must handle them in promises or async/await.

jsx

useEffect(() => {
  const fetchData = async () => {
    try {
      const res = await fetch('/api/data')
      if (!res.ok) throw new Error('API failed')
    } catch (error) {
      console.error(error)
    }
  }
  fetchData()
}, [])

Best Practices

Use multiple small Error Boundaries per feature
Show user-friendly fallback messages
Log errors to a monitoring service (e.g. Sentry)
Don’t hide all errors—fail safely, not silently

Mini Project Step

Wrap your main feature components with Error Boundaries. Add a custom fallback UI that lets users retry or go back to safety without crashing the entire app.

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