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What is not-found.js in Next.js and how do you trigger a 404?

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01

Understand the problem

Rendering 404 UI and the notFound() helper.

nextjsnot-found404routing
02

Attempt it yourself

Sketch your approach before reading the solution — that's what interviews test.

Nudge consolestandby

Stuck? Beam a request up — the console returns a conceptual nudge that guides your logic without spoiling the implementation.

03

Study the solution

not-found.js renders the 404 UI for a segment, and calling the notFound() function from a Server Component (e.g. when a record is missing) renders the nearest not-found boundary and returns a 404 status.

Solution ready — 2 min read

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04

Read the code

404 on a missing record
// app/blog/[slug]/page.tsx
import { notFound } from 'next/navigation';

export default async function Post({ params }) {
  const { slug } = await params;
  const post = await getPost(slug);
  if (!post) notFound();               // → renders not-found.tsx, sends 404
  return <article>{post.title}</article>;
}
05

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