High Next.js Question 185 of 229

How does middleware in Next.js run and what should it not do?

Frontend Master · Speak this in 60–90 seconds · Faridabad & Delhi NCR

PICTURE THIS: DATABASE INDEX

Without indexScan every row

With indexJump to keys

CostWrites slower

Simple meaning

Middleware runs on the Edge before the request hits a page, good for redirects, A/B cookies, and auth gates.

WHY — Next.js instead of guessing?

Why interviewers care about Next.js:

This is a process

question about Next.js.

Panels listen for order,

trade-offs, and what you would actually do on a Frontend project - not buzzwords.

Stay structured

Name the idea, why it exists, then one short example.

Close cleanly

End with when you use it and one common pitfall.

STEPS — What happens step by step?

Before you speak the answer, walk the interviewer through these steps:

1
Middleware runs on the
Edge before the request hits a page, good for redirects, A/B cookies, and auth gates.
2
It should stay tiny:
no heavy Node APIs or large dependencies.
3
Business logic and database
work stay in server components or route handlers.
4
Give an example
One tiny concrete case you can say aloud.
5
Common mistake
What juniors usually get wrong.
6
Close
When you pick this over the alternative.

EXAMPLE — See it in action

Here's a short line you can speak, broken into clear beats:

Say this line

“It should stay tiny: no heavy Node APIs or large dependencies.”

Break into beats

Itshouldstaytinynoheavy

Speaking order

2987408337471632900

Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.

Key takeaway

Middleware runs on the Edge before the request hits a page, good for redirects, A/B cookies, and auth gates. It should stay tiny: no heavy Node APIs or large dependencies.