Client-side error boundaries in NextJS

Introduction

Error boundaries help catch errors in parts of your app so the whole page does not break. They show a fallback UI instead of a blank or broken screen.

When you want to catch errors in a specific part of your UI and show a friendly message.

When you want to prevent the entire app from crashing due to one component's error.

When you want to log errors and still keep the app usable for users.

When you want to isolate errors in complex components like forms or data fetchers.

Syntax

NextJS

import React from 'react';

class ErrorBoundary extends React.Component {
  state = { hasError: false };

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

  render() {
    if (this.state.hasError) {
      return <div>Something went wrong.</div>;
    }

    return this.props.children;
  }
}

Next.js uses React, so error boundaries follow React patterns.

Client-side error boundaries catch errors during rendering, lifecycle methods, and constructors of child components.

Examples

Basic error boundary showing a simple fallback message.

NextJS

import React from 'react';

class ErrorBoundary extends React.Component {
  state = { hasError: false };

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

  render() {
    if (this.state.hasError) {
      return <div>Oops! Something went wrong.</div>;
    }

    return this.props.children;
  }
}

Error boundary that shows the error message and uses ARIA role for accessibility.

NextJS

import React from 'react';

class ErrorBoundary extends React.Component {
  state = { error: null };

  static getDerivedStateFromError(err) {
    return { error: err };
  }

  render() {
    if (this.state.error) {
      return <div role="alert">Error: {this.state.error.message}</div>;
    }

    return this.props.children;
  }
}

Sample Program

This example shows a component that throws an error inside an error boundary. Instead of crashing the whole app, it shows a friendly error message in red.

NextJS

import React from 'react';

class ErrorBoundary extends React.Component {
  state = { hasError: false };

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

  render() {
    if (this.state.hasError) {
      return <div role="alert" style={{ color: 'red' }}>Something went wrong.</div>;
    }

    return this.props.children;
  }
}

function BuggyComponent() {
  throw new Error('Bug!');
}

export default function App() {
  return (
    <main>
      <h1>My Next.js App</h1>
      <ErrorBoundary>
        <BuggyComponent />
      </ErrorBoundary>
    </main>
  );
}

Important Notes

React error boundaries are class components using static getDerivedStateFromError() and optionally componentDidCatch(). Next.js follows the same patterns.

Client-side error boundaries do not catch errors in event handlers or asynchronous code.

Use fallback UI that is accessible and clear to users.

Summary

Error boundaries catch errors in parts of your UI to prevent full app crashes.

They show fallback UI so users see a friendly message instead of a broken screen.

In Next.js, you can create client-side error boundaries using React class components.

Practice

1. What is the main purpose of client-side error boundaries in Next.js?

easy

A. To catch errors in UI components and show a fallback UI instead of crashing the whole app

B. To improve server-side rendering speed

C. To handle database connection errors

D. To optimize image loading performance

Solution

1. Step 1: Understand error boundaries role

   Error boundaries catch errors in parts of the UI to prevent the entire app from crashing.

2. Step 2: Identify their main effect

   They show a fallback UI so users see a friendly message instead of a broken screen.

3. Final Answer:

   To catch errors in UI components and show a fallback UI instead of crashing the whole app -> Option A

4. Quick Check:

   Error boundaries catch UI errors = C [OK]

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

Common Mistakes:

• Confusing error boundaries with server-side features
• Thinking they handle backend or database errors
• Assuming they improve performance directly

2. Which of the following is the correct way to define a client-side error boundary component in Next.js using React hooks?

easy

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

B. class ErrorBoundary extends React.Component { render() { return this.props.children; } }

C. function ErrorBoundary() { return Error; }

D. const ErrorBoundary = () => { return children; }

Solution

1. Step 1: Identify hook-based error boundary pattern

   Client-side error boundaries in Next.js use try/catch inside functional components to catch errors during rendering.

2. Step 2: Check each option

   function ErrorBoundary({ children }) { try { return children; } catch { return ; } } uses try/catch inside a function component returning children or fallback UI, which is correct.

3. Final Answer:

   function ErrorBoundary({ children }) { try { return children; } catch { return <Fallback />; } } -> Option A

4. Quick Check:

   Try/catch in function component = A [OK]

Hint: Use try/catch inside functional component for client error boundaries [OK]

Common Mistakes:

• Using class components instead of functional components
• Not using try/catch to catch errors
• Returning children without error handling

3. Given this client-side error boundary component in Next.js:

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

function BuggyComponent() {
  throw new Error('Bug!');
}

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

What will be rendered on the page?

medium

A. output

B. Error occurred

C. Nothing is rendered

D. The app crashes with an uncaught error

Solution

1. Step 1: Understand error throwing in BuggyComponent

   BuggyComponent throws an error immediately when rendered.

2. Step 2: Check ErrorBoundary behavior

   ErrorBoundary tries to render children inside try block; error triggers catch block returning fallback UI <div>Error occurred</div>.

3. Final Answer:

   <div>Error occurred</div> -> Option B

4. Quick Check:

   Error caught, fallback shown = D [OK]

Hint: Error in child triggers catch, fallback UI renders [OK]

Common Mistakes:

• Expecting the app to crash instead of showing fallback
• Thinking children render despite error
• Confusing output with component name

4. Identify the problem in this client-side error boundary code snippet:

function ErrorBoundary({ children }) {
  try {
    return children;
  } catch (error) {
    console.log(error);
  }
}

export default function App() {
  return (
    <ErrorBoundary>
      <div>Hello</div>
    </ErrorBoundary>
  );
}

What issue will occur when an error happens inside children?

medium

A. The error is caught and fallback UI is shown

B. The error is logged and children still render

C. The app crashes due to syntax error

D. No fallback UI is returned, so the component renders nothing

Solution

1. Step 1: Analyze catch block behavior

   The catch block logs the error but does not return any UI.

2. Step 2: Understand React rendering rules

   Without a return in catch, the component returns undefined, rendering nothing on error.

3. Final Answer:

   No fallback UI is returned, so the component renders nothing -> Option D

4. Quick Check:

   Missing return in catch = renders nothing [OK]

Hint: Always return fallback UI in catch block [OK]

Common Mistakes:

• Forgetting to return fallback UI in catch
• Assuming logging error is enough
• Expecting children to render after error

5. You want to create a client-side error boundary in Next.js that catches errors in nested components and logs the error before showing fallback UI. Which approach correctly combines error catching, logging, and fallback rendering?

hard

A. function ErrorBoundary({ children }) {
try {
return children;
} catch (error) {
return Something went wrong.;
}
}

B. function ErrorBoundary({ children }) {
try {
return children;
} catch {
return Something went wrong.;
}
}

C. function ErrorBoundary({ children }) {
try {
return children;
} catch (error) {
console.error(error);
return Something went wrong.;
}
}

D. function ErrorBoundary({ children }) {
try {
return children;
} catch (error) {
console.log('Error caught');
}
}

Solution

1. Step 1: Check error catching and logging

   function ErrorBoundary({ children }) { try { return children; } catch (error) { console.error(error); return
   Something went wrong.; } } catches error, logs it with console.error, then returns fallback UI.

2. Step 2: Verify fallback UI return

   function ErrorBoundary({ children }) { try { return children; } catch (error) { console.error(error); return
   Something went wrong.
   ; } } returns fallback UI after logging, ensuring user sees message and error is logged.

3. Final Answer:

   function ErrorBoundary({ children }) { try { return children; } catch (error) { console.error(error); return <div>Something went wrong.</div>; } } -> Option C

4. Quick Check:

   Error caught, logged, fallback returned = A [OK]

Hint: Catch error, log it, then return fallback UI [OK]

Common Mistakes:

• Not logging the error before fallback
• Not returning fallback UI after catching error
• Logging without returning fallback UI