Not every [JavaScript](/courses/javascript) error is automatically handled by a [Next.js](/courses/nextjs) `error.tsx` boundary. Error boundaries are primarily designed to catch errors that occur while [React](/courses/reactjs) is rendering the component tree. Errors that happen later inside normal event handlers usually need explicit handling. ### Rendering Error ```tsx function Product() { throw new Error('Unable to render product'); return

Product

; } ``` If this component is inside a [Next.js](/courses/nextjs) error boundary, the boundary can display its fallback UI. ### Event Handler Error ```tsx 'use client'; export default function DeleteButton() { function handleClick() { throw new Error('Delete failed'); } return ( ); } ``` The error happens after rendering, when the user clicks the button. A normal render error boundary should not be your primary way of handling this expected event failure. ### Handle It Explicitly ```tsx 'use client'; import { useState } from 'react'; export default function DeleteButton() { const [error, setError] = useState(''); async function handleClick() { try { await deleteItem(); } catch { setError('Unable to delete this item.'); } } return (

{error &&

{error}

}

); } ``` Now the failure becomes normal UI state. ### What About startTransition? Unhandled errors thrown inside [React](/courses/reactjs) transition work can bubble to an appropriate error boundary in modern React/Next.js behavior. But this should not encourage developers to throw every ordinary event failure. ### Practical Rule ```text Rendering unexpectedly crashes → error boundary User operation fails in a known way → catch/return result → show useful feedback ``` ### Interview-Ready Answer Next.js error boundaries mainly catch errors that occur while React renders their child tree. Normal errors inside event handlers happen after rendering and should generally be handled explicitly with try/catch or application state. Known operation failures should become useful UI feedback instead of deliberately crashing the component tree.