Question 1

RSC vs Client Components — when do you add 'use client' in Next.js 15?

Accepted Answer

**Target Audience:** Engineers preparing for Next.js interviews — assumes what Server Components are. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. **A note on verification:** this needs an RSC runtime, and react-server-dom-webpack is **not installed here**, so nothing below was executed. **Version n

Question 2

Async Server Components & waterfall prevention — fetching without blocking

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes Server Components basics. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. **A note on verification:** unlike most docs in this set, the behaviour here cannot be executed in a unit environment — Server Components need a server runtime and a bundler that understands the RSC protocol. Everything below is reasoned from the docum

Question 3

Error Boundaries with RSC — why can't Server Components catch errors?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes error boundaries and Server Components. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. **A note on verification:** this repo has **no RSC runtime** — r

Question 4

React Server Components vs SSR — what is the real difference?

Accepted Answer

**Target Audience:** Engineers preparing for senior React interviews — assumes SSR. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. **A note on verification:** Server Components need a bundler-integrated server runtime, and react-server-dom-webpack is **not installed in this repo**, so nothing about RSC below w

Question 5

Compare render-as-you-fetch, fetch-on-render, and fetch-then-render.

Accepted Answer

**Target Audience:** Engineers preparing for senior React interviews — assumes Suspense basics. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. All three patterns in section 3 were **executed against React 19.2.8** with the same two 120ms requests, and the timings are the measured ones. Related: Suspense waterfal

Question 6

cache() and fetch memoization — request deduplication in RSC

Accepted Answer

**Target Audience:** Engineers preparing for senior React interviews — assumes Server Components basics. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. **A note on verification:** cache()'s deduplication only operates inside a React server render, which cannot be exercised in a unit environment. What *was* verified here is that the API exists and that outside a server render it delib

Question 7

What are Server Actions and the `"use server"` directive in React 19?

Accepted Answer

**Target Audience:** Engineers preparing for senior React interviews — assumes Actions. **Difficulty:** Hard > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. **A note on verification:** the directive is a bundler-plus-runtime feature and this repo has **no RSC runtime**, so the server half was not executed. The **client half was** — a plain

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