How do middleware work in Next.js?
Interviewer Expectations for this Question
01
Core Competency
Assesses fundamental understanding of Next.js conventions, runtime behavior, and memory/performance considerations.
02
Evaluation Criteria
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
Comprehensive Model Answer
Verified Solution
Middleware in Next.js allows you to run code before a request is completed. You can use it to modify the request or response, redirect users, or perform authentication checks.
// app/middleware.js
import { NextResponse } from "next/server";
export function middleware(request) {
// Perform some logic here
if (request.nextUrl.pathname === "/") {
return NextResponse.redirect(new URL("/home", request.url));
}
return NextResponse.next();
}
You can also specify which paths the middleware should apply to:
// app/middleware.js
export const config = {
matcher: ["/about/:path*", "/blog/:path*"],
};
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.