Question 1

How do you deploy a Next.js app (Vercel vs self-hosted)?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes basic React and App Router familiarity.
**Difficulty:** Medium

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:`. Every behaviour claim was checked against the Next.js docs shipped with the package (written on 16.3.4, re-reviewed against 16.4.2) and, in the **Verified** section, against real output from a build or a running server; each Verified bloc

Question 2

What is after() in Next.js and when should you use it?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes basic React and App Router familiarity.
**Difficulty:** Medium

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:`. Every behaviour claim was checked against the Next.js 16.4.2 docs shipped with the package and, in the **Verified** section, against real output from a build or a running server.

## 1. Why This Even Matters — A Story First

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Question 3

Observability with OpenTelemetry in Next 15 — how is OTEL wired?

Accepted Answer

Install `@vercel/otel`, call `registerOTel` in `instrumentation.ts register()`, and set `experimental.instrumentationHook: true` — Next auto-traces RSC render, fetch, and middleware.

Question 4

How do you handle instrumentation and observability in Next.js (instrumentation.ts)?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes basic React and App Router familiarity.
**Difficulty:** Hard

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:`. Every behaviour claim was checked against the Next.js docs shipped with the package (written on 16.3.4, re-reviewed against 16.4.2) and, in the **Verified** section, against real output from a build or a running server; each Verified block

NEXT.JSDECODED.

Medium

How do you deploy a Next.js app (Vercel vs self-hosted)?

What is after() in Next.js and when should you use it?

Hard

Observability with OpenTelemetry in Next 15 — how is OTEL wired?

How do you handle instrumentation and observability in Next.js (instrumentation.ts)?