Error Boundaries - Catch rendering errors in the component tree and display fallback UI

Q: Why are error boundaries class components and not hooks?

React does not provide a hook equivalent of getDerivedStateFromError or componentDidCatch. These lifecycle methods are only available in class components. Use the react-error-boundary library if you prefer a hook-friendly wrapper API.

Q: What is the difference between getDerivedStateFromError and componentDidCatch?

getDerivedStateFromError runs during the render phase to update state and trigger the fallback UI. It must be a pure function. componentDidCatch runs after the commit phase for side effects like logging errors to Sentry. Use both: one for showing the fallback, one for reporting.

Q: How do resetKeys work for automatic error recovery?

When resetKeys change (e.g., userId changes), the boundary automatically resets and retries rendering. This pairs well with route parameter changes to recover from stale errors.

Q: How do you type an error boundary component in TypeScript?

Type state as { error: Error | null } to preserve the error object for the fallback. Use ErrorInfo from React for componentDidCatch's second parameter.

Q: What is error.digest in Next.js error boundaries?

error.digest is a hashed error identifier generated by Next.js for server-side errors. It is safe to display to users because it does not expose stack traces or sensitive details. In development, the full error is shown instead.

Recipe

import { Component, type ErrorInfo, type ReactNode } from "react";
 
class ErrorBoundary extends Component<
  { children: ReactNode; fallback: ReactNode },
  { hasError: boolean }
> {
  state = { hasError: false };
 
  static getDerivedStateFromError(): { hasError: boolean } {
    return { hasError: true };
  }
 
  componentDidCatch(error: Error, info: ErrorInfo) {
    console.error("ErrorBoundary caught:", error, info.componentStack);
  }
 
  render() {
    if (this.state.hasError) return this.props.fallback;
    return this.props.children;
  }
}
 
// Usage
<ErrorBoundary fallback={<p>Something went wrong.</p>}>
  <RiskyComponent />
</ErrorBoundary>

When to reach for this: Wrap any component subtree that might throw during rendering. Essential around data-fetching components, third-party widgets, user-generated content renderers, and route-level layouts.

Working Example

import {
  Component,
  useState,
  useCallback,
  type ErrorInfo,
  type ReactNode,
} from "react";
 
// --- Full-featured error boundary with recovery ---
 
interface ErrorBoundaryProps {
  children: ReactNode;
  fallback?: ReactNode;
  onError?: (error: Error, info: ErrorInfo) => void;
  renderFallback?: (props: {
    error: Error;
    reset: () => void;
  }) => ReactNode;
  resetKeys?: unknown[];
}
 
interface ErrorBoundaryState {
  error: Error | null;
}
 
class ErrorBoundary extends Component<ErrorBoundaryProps, ErrorBoundaryState> {
  state: ErrorBoundaryState = { error: null };
 
  static getDerivedStateFromError(error: Error): ErrorBoundaryState {
    return { error };
  }
 
  componentDidCatch(error: Error, info: ErrorInfo) {
    this.props.onError?.(error, info);
  }
 
  componentDidUpdate(prevProps: ErrorBoundaryProps) {
    if (this.state.error && prevProps.resetKeys !== this.props.resetKeys) {
      // If resetKeys changed, attempt recovery
      const changed = this.props.resetKeys?.some(
        (key, i) => key !== prevProps.resetKeys?.[i]
      );
      if (changed) this.reset();
    }
  }
 
  reset = () => {
    this.setState({ error: null });
  };
 
  render() {
    const { error } = this.state;
    const { children, fallback, renderFallback } = this.props;
 
    if (error) {
      if (renderFallback) {
        return renderFallback({ error, reset: this.reset });
      }
      return fallback ?? <p>Something went wrong.</p>;
    }
 
    return children;
  }
}
 
// --- Usage with recovery UI ---
 
function UserProfile({ userId }: { userId: string }) {
  return (
    <ErrorBoundary
      resetKeys={[userId]}
      onError={(error) => {
        // Report to error tracking service
        reportToSentry(error);
      }}
      renderFallback={({ error, reset }) => (
        <div className="p-6 bg-red-50 rounded-lg text-center">
          <h3 className="text-red-800 font-semibold">Failed to load profile</h3>
          <p className="text-red-600 mt-2">{error.message}</p>
          <button
            onClick={reset}
            className="mt-4 px-4 py-2 bg-red-600 text-white rounded hover:bg-red-700"
          >
            Try Again
          </button>
        </div>
      )}
    >
      <ProfileContent userId={userId} />
    </ErrorBoundary>
  );
}
 
// --- Granular error boundaries per section ---
 
function DashboardPage() {
  return (
    <div className="grid grid-cols-2 gap-4">
      <ErrorBoundary fallback={<WidgetError name="Revenue" />}>
        <RevenueChart />
      </ErrorBoundary>
      <ErrorBoundary fallback={<WidgetError name="Users" />}>
        <UserStats />
      </ErrorBoundary>
      <ErrorBoundary fallback={<WidgetError name="Activity" />}>
        <ActivityFeed />
      </ErrorBoundary>
    </div>
  );
}
 
function WidgetError({ name }: { name: string }) {
  return (
    <div className="p-4 border border-red-200 rounded bg-red-50 text-red-700">
      {name} widget failed to load.
    </div>
  );
}

What this demonstrates:

Render-prop fallback with access to the error object and a reset function
resetKeys prop that auto-resets the boundary when dependencies change (e.g., route params)
Error reporting hook (onError) for Sentry or similar services
Granular boundaries so one broken widget doesn't take down the entire page

Deep Dive

How It Works

Error boundaries are class components that implement static getDerivedStateFromError() or componentDidCatch().
getDerivedStateFromError runs during render to set error state and trigger fallback UI.
componentDidCatch runs after commit for side effects like error logging.
Error boundaries catch errors thrown during rendering, in lifecycle methods, and in constructors of their child tree.
They do NOT catch errors in event handlers, async code, server-side rendering, or errors thrown in the boundary itself.

Parameters & Return Values

Lifecycle Method	When Called	Purpose
`getDerivedStateFromError(error)`	During render	Return new state to trigger fallback UI
`componentDidCatch(error, info)`	After commit	Side effects: logging, error reporting
`info.componentStack`	In `componentDidCatch`	String showing the component tree path

Variations

Hook-based error boundary wrapper - use a package or thin wrapper for hook ergonomics:

// With react-error-boundary (popular library)
import { ErrorBoundary } from "react-error-boundary";
 
function App() {
  return (
    <ErrorBoundary
      FallbackComponent={ErrorFallback}
      onReset={() => queryClient.invalidateQueries()}
      resetKeys={[routeKey]}
    >
      <AppContent />
    </ErrorBoundary>
  );
}
 
function ErrorFallback({
  error,
  resetErrorBoundary,
}: {
  error: Error;
  resetErrorBoundary: () => void;
}) {
  return (
    <div role="alert">
      <p>Error: {error.message}</p>
      <button onClick={resetErrorBoundary}>Retry</button>
    </div>
  );
}

Nested boundaries with different granularity:

// Page-level boundary catches everything
<ErrorBoundary fallback={<FullPageError />}>
  <Layout>
    {/* Section-level boundaries isolate failures */}
    <ErrorBoundary fallback={<SectionError />}>
      <Sidebar />
    </ErrorBoundary>
    <ErrorBoundary fallback={<SectionError />}>
      <MainContent />
    </ErrorBoundary>
  </Layout>
</ErrorBoundary>

TypeScript Notes

Type the state as { error: Error | null } rather than { hasError: boolean } to preserve the error object for the fallback.
Use ErrorInfo from React for the componentDidCatch second parameter.
The componentStack property on ErrorInfo is a string, not a structured object.

Gotchas

Event handler errors are not caught - Error boundaries only catch errors during React rendering. An onClick that throws will not be caught. Fix: Use try/catch in event handlers and set local error state.
Async errors are not caught - Promises that reject inside useEffect or event handlers are not caught. Fix: Catch async errors and either set local state or re-throw during render (e.g., store in state and throw in render).
No hook-based error boundaries - React does not provide a hook equivalent of getDerivedStateFromError. Fix: Use the class component pattern or the react-error-boundary library.
Error boundary itself throwing - If the error boundary's own render method throws, it propagates to the nearest parent boundary. Fix: Keep error boundary render methods simple. Never throw in the fallback UI.
Recovery without unmount - Resetting hasError to false without remounting children may leave them in a broken state. Fix: Use a key prop on the children wrapper to force remount on reset.

Alternatives

Approach	Trade-off
Error boundaries	Catches render errors; requires class component
`react-error-boundary`	Hook-friendly API, `resetKeys`; extra dependency
Try/catch in event handlers	Manual; doesn't catch render errors
Suspense with error handling	Handles async loading errors via thrown promises
Global `window.onerror`	Catches uncaught errors; no React-specific recovery

Real-World Example

From a production Next.js 15 / React 19 SaaS application (SystemsArchitect.io).

// Production example: Next.js error.tsx with logging, retry, and full-page reload fallback
// File: app/error.tsx
'use client';
 
import { useEffect } from 'react';
 
export default function Error({
  error,
  reset,
}: {
  error: Error & { digest?: string };
  reset: () => void;
}) {
  useEffect(() => {
    // Log to external error tracking service
    console.error('Application error:', error);
    // reportToSentry(error);
  }, [error]);
 
  return (
    <div className="flex min-h-screen items-center justify-center">
      <div className="text-center space-y-4">
        <h2 className="text-2xl font-bold">Something went wrong</h2>
        {error.digest && (
          <p className="text-sm text-gray-500">Error ID: {error.digest}</p>
        )}
        <div className="flex gap-3 justify-center">
          <button
            onClick={reset}
            className="px-4 py-2 bg-blue-600 text-white rounded hover:bg-blue-700"
          >
            Try again
          </button>
          <button
            onClick={() => window.location.href = '/'}
            className="px-4 py-2 border rounded hover:bg-gray-50"
          >
            Go home
          </button>
        </div>
      </div>
    </div>
  );
}

What this demonstrates in production:

error.tsx is a Next.js App Router convention that automatically wraps the page in an error boundary. You do not need to write a class-based error boundary yourself.
The useEffect logs the error on mount. This is the correct place to send errors to Sentry or a similar service. Do not log in the render body because it runs during React's render phase.
reset() re-renders the route segment, which retries the failed component. This works well for transient errors like network failures or race conditions.
error.digest is a hashed error identifier that Next.js generates for server-side errors. It is safe to display to users (it does not expose stack traces or sensitive details). In development, the full error is shown instead.
The "Go home" button uses window.location.href instead of router.push() as a deliberate choice. If the error corrupted the React tree or client-side router state, router.push() might fail or render the same broken page. A full page reload via window.location.href guarantees a clean start.
This error.tsx must be a Client Component ('use client'). Error boundaries require client-side React to catch and recover from errors.

FAQs

What is an error boundary and what errors does it catch?

An error boundary is a class component that catches errors during rendering, lifecycle methods, and constructors of its child tree.
It displays a fallback UI instead of crashing the entire app.
It does NOT catch errors in event handlers, async code, SSR, or errors in the boundary itself.

Why are error boundaries class components and not hooks?

React does not provide a hook equivalent of getDerivedStateFromError or componentDidCatch.
These lifecycle methods are only available in class components.
Use the react-error-boundary library if you prefer a hook-friendly wrapper API.

What is the difference between `getDerivedStateFromError` and `componentDidCatch`?

getDerivedStateFromError runs during the render phase to update state and trigger the fallback UI. It must be a pure function.
componentDidCatch runs after the commit phase for side effects like logging errors to Sentry.
Use both: one for showing the fallback, one for reporting.

How do `resetKeys` work for automatic error recovery?

<ErrorBoundary
  resetKeys={[userId]}
  renderFallback={({ error, reset }) => (
    <div>
      <p>{error.message}</p>
      <button onClick={reset}>Retry</button>
    </div>
  )}
>
  <ProfileContent userId={userId} />
</ErrorBoundary>

When resetKeys change (e.g., userId changes), the boundary automatically resets and retries rendering.
This pairs well with route parameter changes to recover from stale errors.

Gotcha: Why don't error boundaries catch errors in event handlers?

Error boundaries only catch errors thrown during React's rendering lifecycle.
An onClick handler that throws does not interrupt rendering; it throws in the browser's event loop.
Fix: use try/catch inside event handlers and set local error state.

Gotcha: What happens if the error boundary's own render method throws?

The error propagates to the nearest parent error boundary.
If no parent boundary exists, the entire app crashes.
Fix: keep error boundary render methods and fallback UI simple. Never throw in the fallback.

How do you type an error boundary component in TypeScript?

interface ErrorBoundaryState {
  error: Error | null;
}
 
class ErrorBoundary extends Component<ErrorBoundaryProps, ErrorBoundaryState> {
  state: ErrorBoundaryState = { error: null };
 
  static getDerivedStateFromError(error: Error): ErrorBoundaryState {
    return { error };
  }
}

Type state as { error: Error | null } to preserve the error object for the fallback.
Use ErrorInfo from React for componentDidCatch's second parameter.

What is `error.digest` in Next.js error boundaries?

error.digest is a hashed error identifier generated by Next.js for server-side errors.
It is safe to display to users because it does not expose stack traces or sensitive details.
In development, the full error is shown instead.

Why does the Next.js `error.tsx` "Go home" button use `window.location.href` instead of `router.push()`?

If the error corrupted the React tree or client-side router state, router.push() might fail or render the same broken page.
window.location.href triggers a full page reload, guaranteeing a clean start.
This is a deliberate production safety pattern.

How should you structure error boundaries for granular error isolation?

Place a page-level boundary to catch any uncaught errors as a last resort.
Place section-level boundaries around individual widgets or features so one failure does not take down the entire page.
Each boundary can show its own localized fallback UI.

How do you reset an error boundary without leaving children in a broken state?

Simply resetting hasError to false re-renders the same children, which may still be broken.
Fix: use a key prop on the children wrapper to force a full unmount and remount on reset.
This ensures children start fresh with clean state.

Suspense - Loading state boundaries that pair with error boundaries
State Machines - Model error states explicitly in state transitions
Composition - Error boundaries use the composition pattern with children

Recipe

import { Component, type ErrorInfo, type ReactNode } from "react";
 
class ErrorBoundary extends Component<
  { children: ReactNode; fallback: ReactNode },
  { hasError: boolean }
> {
  state = { hasError: false };
 
  static getDerivedStateFromError(): { hasError: boolean } {
    return { hasError: true };
  }
 
  componentDidCatch(error: Error, info: ErrorInfo) {
    console.error("ErrorBoundary caught:", error, info.componentStack);
  }
 
  render() {
    if (this.state.hasError) return this.props.fallback;
    return this.props.children;
  }
}
 
// Usage
<ErrorBoundary fallback={<p>Something went wrong.</p>}>
  <RiskyComponent />
</ErrorBoundary>

Working Example

import {
  Component,
  useState,
  useCallback,
  type ErrorInfo,
  type ReactNode,
} from "react";
 
// --- Full-featured error boundary with recovery ---
 
interface ErrorBoundaryProps {
  children: ReactNode;
  fallback?: ReactNode;
  onError?: (error: Error, info: ErrorInfo) => void;
  renderFallback?: (props: {
    error: Error;
    reset: () => void;
  }) => ReactNode;
  resetKeys?: unknown[];
}
 
interface ErrorBoundaryState {
  error: Error | null;
}
 
class ErrorBoundary extends Component<ErrorBoundaryProps, ErrorBoundaryState> {
  state: ErrorBoundaryState = { error: null };
 
  static getDerivedStateFromError(error: Error): ErrorBoundaryState {
    return { error };
  }
 
  componentDidCatch(error: Error, info: ErrorInfo) {
    this.props.onError?.(error, info);
  }
 
  componentDidUpdate(prevProps: ErrorBoundaryProps) {
    if (this.state.error && prevProps.resetKeys !== this.props.resetKeys) {
      // If resetKeys changed, attempt recovery
      const changed = this.props.resetKeys?.some(
        (key, i) => key !== prevProps.resetKeys?.[i]
      );
      if (changed) this.reset();
    }
  }
 
  reset = () => {
    this.setState({ error: null });
  };
 
  render() {
    const { error } = this.state;
    const { children, fallback, renderFallback } = this.props;
 
    if (error) {
      if (renderFallback) {
        return renderFallback({ error, reset: this.reset });
      }
      return fallback ?? <p>Something went wrong.</p>;
    }
 
    return children;
  }
}
 
// --- Usage with recovery UI ---
 
function UserProfile({ userId }: { userId: string }) {
  return (
    <ErrorBoundary
      resetKeys={[userId]}
      onError={(error) => {
        // Report to error tracking service
        reportToSentry(error);
      }}
      renderFallback={({ error, reset }) => (
        <div className="p-6 bg-red-50 rounded-lg text-center">
          <h3 className="text-red-800 font-semibold">Failed to load profile</h3>
          <p className="text-red-600 mt-2">{error.message}</p>
          <button
            onClick={reset}
            className="mt-4 px-4 py-2 bg-red-600 text-white rounded hover:bg-red-700"
          >
            Try Again
          </button>
        </div>
      )}
    >
      <ProfileContent userId={userId} />
    </ErrorBoundary>
  );
}
 
// --- Granular error boundaries per section ---
 
function DashboardPage() {
  return (
    <div className="grid grid-cols-2 gap-4">
      <ErrorBoundary fallback={<WidgetError name="Revenue" />}>
        <RevenueChart />
      </ErrorBoundary>
      <ErrorBoundary fallback={<WidgetError name="Users" />}>
        <UserStats />
      </ErrorBoundary>
      <ErrorBoundary fallback={<WidgetError name="Activity" />}>
        <ActivityFeed />
      </ErrorBoundary>
    </div>
  );
}
 
function WidgetError({ name }: { name: string }) {
  return (
    <div className="p-4 border border-red-200 rounded bg-red-50 text-red-700">
      {name} widget failed to load.
    </div>
  );
}

What this demonstrates:

Render-prop fallback with access to the error object and a reset function
resetKeys prop that auto-resets the boundary when dependencies change (e.g., route params)
Error reporting hook (onError) for Sentry or similar services
Granular boundaries so one broken widget doesn't take down the entire page

Deep Dive

How It Works

Error boundaries are class components that implement static getDerivedStateFromError() or componentDidCatch().
getDerivedStateFromError runs during render to set error state and trigger fallback UI.
componentDidCatch runs after commit for side effects like error logging.
Error boundaries catch errors thrown during rendering, in lifecycle methods, and in constructors of their child tree.
They do NOT catch errors in event handlers, async code, server-side rendering, or errors thrown in the boundary itself.

Parameters & Return Values

Lifecycle Method	When Called	Purpose
`getDerivedStateFromError(error)`	During render	Return new state to trigger fallback UI
`componentDidCatch(error, info)`	After commit	Side effects: logging, error reporting
`info.componentStack`	In `componentDidCatch`	String showing the component tree path

Variations

Hook-based error boundary wrapper - use a package or thin wrapper for hook ergonomics:

// With react-error-boundary (popular library)
import { ErrorBoundary } from "react-error-boundary";
 
function App() {
  return (
    <ErrorBoundary
      FallbackComponent={ErrorFallback}
      onReset={() => queryClient.invalidateQueries()}
      resetKeys={[routeKey]}
    >
      <AppContent />
    </ErrorBoundary>
  );
}
 
function ErrorFallback({
  error,
  resetErrorBoundary,
}: {
  error: Error;
  resetErrorBoundary: () => void;
}) {
  return (
    <div role="alert">
      <p>Error: {error.message}</p>
      <button onClick={resetErrorBoundary}>Retry</button>
    </div>
  );
}

Nested boundaries with different granularity:

// Page-level boundary catches everything
<ErrorBoundary fallback={<FullPageError />}>
  <Layout>
    {/* Section-level boundaries isolate failures */}
    <ErrorBoundary fallback={<SectionError />}>
      <Sidebar />
    </ErrorBoundary>
    <ErrorBoundary fallback={<SectionError />}>
      <MainContent />
    </ErrorBoundary>
  </Layout>
</ErrorBoundary>

TypeScript Notes

Type the state as { error: Error | null } rather than { hasError: boolean } to preserve the error object for the fallback.
Use ErrorInfo from React for the componentDidCatch second parameter.
The componentStack property on ErrorInfo is a string, not a structured object.

Gotchas

Event handler errors are not caught - Error boundaries only catch errors during React rendering. An onClick that throws will not be caught. Fix: Use try/catch in event handlers and set local error state.
Async errors are not caught - Promises that reject inside useEffect or event handlers are not caught. Fix: Catch async errors and either set local state or re-throw during render (e.g., store in state and throw in render).
No hook-based error boundaries - React does not provide a hook equivalent of getDerivedStateFromError. Fix: Use the class component pattern or the react-error-boundary library.
Error boundary itself throwing - If the error boundary's own render method throws, it propagates to the nearest parent boundary. Fix: Keep error boundary render methods simple. Never throw in the fallback UI.
Recovery without unmount - Resetting hasError to false without remounting children may leave them in a broken state. Fix: Use a key prop on the children wrapper to force remount on reset.

Alternatives

Approach	Trade-off
Error boundaries	Catches render errors; requires class component
`react-error-boundary`	Hook-friendly API, `resetKeys`; extra dependency
Try/catch in event handlers	Manual; doesn't catch render errors
Suspense with error handling	Handles async loading errors via thrown promises
Global `window.onerror`	Catches uncaught errors; no React-specific recovery

Real-World Example

From a production Next.js 15 / React 19 SaaS application (SystemsArchitect.io).

// Production example: Next.js error.tsx with logging, retry, and full-page reload fallback
// File: app/error.tsx
'use client';
 
import { useEffect } from 'react';
 
export default function Error({
  error,
  reset,
}: {
  error: Error & { digest?: string };
  reset: () => void;
}) {
  useEffect(() => {
    // Log to external error tracking service
    console.error('Application error:', error);
    // reportToSentry(error);
  }, [error]);
 
  return (
    <div className="flex min-h-screen items-center justify-center">
      <div className="text-center space-y-4">
        <h2 className="text-2xl font-bold">Something went wrong</h2>
        {error.digest && (
          <p className="text-sm text-gray-500">Error ID: {error.digest}</p>
        )}
        <div className="flex gap-3 justify-center">
          <button
            onClick={reset}
            className="px-4 py-2 bg-blue-600 text-white rounded hover:bg-blue-700"
          >
            Try again
          </button>
          <button
            onClick={() => window.location.href = '/'}
            className="px-4 py-2 border rounded hover:bg-gray-50"
          >
            Go home
          </button>
        </div>
      </div>
    </div>
  );
}

What this demonstrates in production:

error.tsx is a Next.js App Router convention that automatically wraps the page in an error boundary. You do not need to write a class-based error boundary yourself.
The useEffect logs the error on mount. This is the correct place to send errors to Sentry or a similar service. Do not log in the render body because it runs during React's render phase.
reset() re-renders the route segment, which retries the failed component. This works well for transient errors like network failures or race conditions.
error.digest is a hashed error identifier that Next.js generates for server-side errors. It is safe to display to users (it does not expose stack traces or sensitive details). In development, the full error is shown instead.
The "Go home" button uses window.location.href instead of router.push() as a deliberate choice. If the error corrupted the React tree or client-side router state, router.push() might fail or render the same broken page. A full page reload via window.location.href guarantees a clean start.
This error.tsx must be a Client Component ('use client'). Error boundaries require client-side React to catch and recover from errors.

FAQs

What is an error boundary and what errors does it catch?

An error boundary is a class component that catches errors during rendering, lifecycle methods, and constructors of its child tree.
It displays a fallback UI instead of crashing the entire app.
It does NOT catch errors in event handlers, async code, SSR, or errors in the boundary itself.

Why are error boundaries class components and not hooks?

React does not provide a hook equivalent of getDerivedStateFromError or componentDidCatch.
These lifecycle methods are only available in class components.
Use the react-error-boundary library if you prefer a hook-friendly wrapper API.

What is the difference between `getDerivedStateFromError` and `componentDidCatch`?

getDerivedStateFromError runs during the render phase to update state and trigger the fallback UI. It must be a pure function.
componentDidCatch runs after the commit phase for side effects like logging errors to Sentry.
Use both: one for showing the fallback, one for reporting.

How do `resetKeys` work for automatic error recovery?

<ErrorBoundary
  resetKeys={[userId]}
  renderFallback={({ error, reset }) => (
    <div>
      <p>{error.message}</p>
      <button onClick={reset}>Retry</button>
    </div>
  )}
>
  <ProfileContent userId={userId} />
</ErrorBoundary>

When resetKeys change (e.g., userId changes), the boundary automatically resets and retries rendering.
This pairs well with route parameter changes to recover from stale errors.

Gotcha: Why don't error boundaries catch errors in event handlers?

Error boundaries only catch errors thrown during React's rendering lifecycle.
An onClick handler that throws does not interrupt rendering; it throws in the browser's event loop.
Fix: use try/catch inside event handlers and set local error state.

Gotcha: What happens if the error boundary's own render method throws?

The error propagates to the nearest parent error boundary.
If no parent boundary exists, the entire app crashes.
Fix: keep error boundary render methods and fallback UI simple. Never throw in the fallback.

How do you type an error boundary component in TypeScript?

interface ErrorBoundaryState {
  error: Error | null;
}
 
class ErrorBoundary extends Component<ErrorBoundaryProps, ErrorBoundaryState> {
  state: ErrorBoundaryState = { error: null };
 
  static getDerivedStateFromError(error: Error): ErrorBoundaryState {
    return { error };
  }
}

Type state as { error: Error | null } to preserve the error object for the fallback.
Use ErrorInfo from React for componentDidCatch's second parameter.

What is `error.digest` in Next.js error boundaries?

error.digest is a hashed error identifier generated by Next.js for server-side errors.
It is safe to display to users because it does not expose stack traces or sensitive details.
In development, the full error is shown instead.

Why does the Next.js `error.tsx` "Go home" button use `window.location.href` instead of `router.push()`?

If the error corrupted the React tree or client-side router state, router.push() might fail or render the same broken page.
window.location.href triggers a full page reload, guaranteeing a clean start.
This is a deliberate production safety pattern.

How should you structure error boundaries for granular error isolation?

Place a page-level boundary to catch any uncaught errors as a last resort.
Place section-level boundaries around individual widgets or features so one failure does not take down the entire page.
Each boundary can show its own localized fallback UI.

How do you reset an error boundary without leaving children in a broken state?

Simply resetting hasError to false re-renders the same children, which may still be broken.
Fix: use a key prop on the children wrapper to force a full unmount and remount on reset.
This ensures children start fresh with clean state.

Suspense - Loading state boundaries that pair with error boundaries
State Machines - Model error states explicitly in state transitions
Composition - Error boundaries use the composition pattern with children

Error Boundaries - Catch rendering errors in the component tree and display fallback UI

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Error Boundaries - Catch rendering errors in the component tree and display fallback UI