Q: What is the difference between build-time and runtime environment variables in Next.js?

NEXT_PUBLIC_ vars are **inlined at build time**, so changing them requires a **rebuild**. Server-only vars read from process.env at **runtime** can change per environment **without rebuilding** (for dynamically-rendered code). This matters for **Docker images promoted across environments**. <rect class='d-box-muted' x='20' y='30' width='200

Question 1

What is the difference between build-time and runtime environment variables in Next.js?

Accepted Answer

NEXT_PUBLIC_ vars are **inlined at build time**, so changing them requires a **rebuild**. Server-only vars read from process.env at **runtime** can change per environment **without rebuilding** (for dynamically-rendered code). This matters for **Docker images promoted across environments**.

Question 2

How do you enable and evaluate the React Compiler in Next.js 16?

Accepted Answer

**Target Audience:** Frontend engineers preparing for Next.js interviews — assumes you know React state and re-rendering.
**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 (`reactCompiler`, `turbopackRustReactCompiler`, the version 16 guide) and, in the **Verified** section, against three builds of the same 16.4.2 lab app with render counts re

NEXT.JSDECODED.

Medium

What is the difference between build-time and runtime environment variables in Next.js?

How do you enable and evaluate the React Compiler in Next.js 16?