Why error boundaries matter in NextJS - See It in Action

Why Error Boundaries Matter in Next.js

📖 Scenario: Imagine you are building a blog website using Next.js. Sometimes, parts of your page might break because of unexpected errors in components. You want to make sure that if one part breaks, the rest of the page still works and shows a friendly message instead of a blank screen.

🎯 Goal: Build a simple Next.js component that uses an error boundary to catch errors in a child component and display a fallback UI. This helps keep the app running smoothly even if some parts fail.

📋 What You'll Learn

Create a React error boundary component called ErrorBoundary using a class component.

Add a state variable hasError initialized to false in ErrorBoundary.

Implement the static getDerivedStateFromError(error) method to update hasError to true when an error occurs.

Render a fallback UI with a message Something went wrong. when hasError is true.

Use the ErrorBoundary component to wrap a child component called BuggyComponent that throws an error.

Ensure the rest of the page content outside BuggyComponent still renders normally.

💡 Why This Matters

🌍 Real World

Web apps often have parts that can fail due to bugs or network issues. Error boundaries help keep the app usable by catching these errors and showing fallback content.

💼 Career

Understanding error boundaries is important for frontend developers to build resilient React and Next.js applications that handle errors gracefully.

1

Create the BuggyComponent that throws an error

Create a functional component called BuggyComponent that throws an error with the message "I crashed!" when rendered.

NextJS

# Your code here
// Create BuggyComponent that throws an error

Hint

This component simulates a crash by throwing an error when it tries to render.

2

Create the ErrorBoundary class component with state

Create a class component called ErrorBoundary that extends React.Component. Add a constructor that initializes this.state = { hasError: false }.

NextJS

function BuggyComponent() {
  throw new Error("I crashed!");
}

// Your code here
// Create ErrorBoundary class component with state hasError false

Hint

The constructor sets up the initial state to track if an error happened.

3

Add error handling method and fallback UI

Inside ErrorBoundary, add the static method getDerivedStateFromError(error) that returns { hasError: true }. Also, add a render() method that returns <h2>Something went wrong.</h2> if this.state.hasError is true, otherwise renders this.props.children.

NextJS

function BuggyComponent() {
  throw new Error("I crashed!");
}

import React from 'react';

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

  // Your code here
  // Add getDerivedStateFromError and render methods
}

Hint

This method updates the state when an error happens. The render method shows a fallback message or the child components.

4

Use ErrorBoundary to wrap BuggyComponent in a Next.js page

Create a default export functional component called Page that returns a fragment with a heading <h1>My Blog</h1>, then uses <ErrorBoundary> to wrap <BuggyComponent />, and finally a paragraph <p>Welcome to the blog!</p> outside the error boundary.

NextJS

function BuggyComponent() {
  throw new Error("I crashed!");
}

import React from 'react';

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

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

  render() {
    if (this.state.hasError) {
      return Something went wrong.;
    }
    return this.props.children;
  }
}

// Your code here
// Create Page component that uses ErrorBoundary to wrap BuggyComponent

Hint

This final step shows how to use the error boundary to protect the buggy component and keep the rest of the page visible.

Practice

1. What is the main purpose of error boundaries in a Next.js application?

easy

A. To catch JavaScript errors in components and display a fallback UI

B. To improve SEO by optimizing page metadata

C. To handle server-side rendering errors automatically

D. To manage user authentication and sessions

Solution

1. Step 1: Understand error boundaries role

   Error boundaries catch errors in React components during rendering, lifecycle methods, and constructors.

2. Step 2: Identify their main benefit

   They prevent the whole app from crashing by showing a fallback UI instead of a broken screen.

3. Final Answer:

   To catch JavaScript errors in components and display a fallback UI -> Option A

4. Quick Check:

   Error boundaries catch errors = B [OK]

Hint: Error boundaries catch errors and show fallback UI [OK]

Common Mistakes:

• Confusing error boundaries with authentication
• Thinking error boundaries improve SEO
• Assuming error boundaries handle server errors automatically

2. Which of the following is the correct way to define an error boundary component in Next.js using React functional components?

easy

A. class ErrorBoundary extends React.Component { constructor() { super(); this.state = { hasError: false }; } componentDidCatch() { this.setState({ hasError: true }); } render() { if (this.state.hasError) return Error occurred; return this.props.children; } }

B. function ErrorBoundary({ children }) { const [hasError, setHasError] = React.useState(false); if (hasError) return Error; return children; }

C. function ErrorBoundary({ children }) { try { return children; } catch { return Error; } }

D. class ErrorBoundary extends React.Component { state = { error: null }; render() { if (this.state.error) return Error; return this.props.children; } }

Solution

1. Step 1: Recall error boundary implementation

   Error boundaries must be class components with lifecycle methods like componentDidCatch to catch errors.

2. Step 2: Check options for correct syntax

   class ErrorBoundary extends React.Component { constructor() { super(); this.state = { hasError: false }; } componentDidCatch() { this.setState({ hasError: true }); } render() { if (this.state.hasError) return <div>Error occurred</div>; return this.props.children; } } correctly defines a class component with constructor, state, componentDidCatch, and render method.

3. Final Answer:

   class ErrorBoundary extends React.Component { constructor() { super(); this.state = { hasError: false }; } componentDidCatch() { this.setState({ hasError: true }); } render() { if (this.state.hasError) return <div>Error occurred</div>; return this.props.children; } } -> Option A

4. Quick Check:

   Error boundaries require class + componentDidCatch = C [OK]

Hint: Error boundaries must be class components with componentDidCatch [OK]

Common Mistakes:

• Trying to create error boundaries as functional components
• Missing componentDidCatch lifecycle method
• Not initializing state to track errors

3. Given the following error boundary component and a child component that throws an error, what will be rendered?

class ErrorBoundary extends React.Component {
  constructor(props) {
    super(props);
    this.state = { hasError: false };
  }
  componentDidCatch(error, info) {
    this.setState({ hasError: true });
  }
  render() {
    if (this.state.hasError) {
      return <h1>Something went wrong.</h1>;
    }
    return this.props.children;
  }
}

function BuggyComponent() {
  throw new Error('Bug!');
  return <div>No bugs</div>;
}

// Usage
<ErrorBoundary>
  <BuggyComponent />
</ErrorBoundary>

medium

A. Uncaught Error: Bug!

B. No bugs

C. Something went wrong.

D. Blank screen

Solution

1. Step 1: Understand error throwing in child

   BuggyComponent throws an error immediately when rendered.

2. Step 2: Check error boundary response

   ErrorBoundary catches the error in componentDidCatch and sets hasError to true, rendering fallback UI.

3. Final Answer:

   <h1>Something went wrong.</h1> -> Option C

4. Quick Check:

   Error caught, fallback UI shown = A [OK]

Hint: ErrorBoundary shows fallback UI when child throws error [OK]

Common Mistakes:

• Expecting child component output despite error
• Thinking error is uncaught and crashes app
• Assuming blank screen instead of fallback UI

4. You have this error boundary component but it does not catch errors as expected. What is the likely problem?

function ErrorBoundary({ children }) {
  try {
    return children;
  } catch (error) {
    return <div>Error occurred</div>;
  }
}

medium

A. Try-catch works fine for error boundaries in functional components

B. Error boundaries must be class components with componentDidCatch method

C. You forgot to wrap children in a React.Fragment

D. You need to use useErrorBoundary hook instead

Solution

1. Step 1: Analyze error boundary implementation

   Try-catch inside a functional component does not catch errors during rendering lifecycle in React.

2. Step 2: Recall React error boundary requirements

   Error boundaries must be class components implementing componentDidCatch lifecycle method to catch errors properly.

3. Final Answer:

   Error boundaries must be class components with componentDidCatch method -> Option B

4. Quick Check:

   Functional try-catch won't catch render errors = A [OK]

Hint: Error boundaries require class + componentDidCatch, not try-catch [OK]

Common Mistakes:

• Using try-catch in functional components expecting error boundary behavior
• Assuming React has a useErrorBoundary hook
• Thinking wrapping children in fragments fixes error catching

5. You want to add a reset button in your error boundary to let users try again after an error. Which approach correctly implements this behavior?

hard

A. Use a useEffect hook to reset error state automatically after 5 seconds

B. Reload the entire page using window.location.reload() when the button is clicked

C. Wrap the reset button in a try-catch block to prevent errors

D. Add a button that calls this.setState({ hasError: false }) inside the error boundary's fallback UI

Solution

1. Step 1: Understand reset behavior in error boundaries

   Resetting error state allows the component tree to re-render normally after an error.

2. Step 2: Identify correct reset method

   Calling this.setState({ hasError: false }) inside the error boundary resets the error state and shows children again.

3. Final Answer:

   Add a button that calls this.setState({ hasError: false }) inside the error boundary's fallback UI -> Option D

4. Quick Check:

   Reset error state with setState = D [OK]

Hint: Reset error by setting hasError false in state [OK]

Common Mistakes:

• Reloading page instead of resetting state
• Using try-catch around reset button unnecessarily
• Relying on automatic reset with useEffect without user action