Server-only modules in NextJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are server-only modules in Next.js?

Server-only modules are files or code that run only on the server side in Next.js. They never get sent to the browser, keeping sensitive logic or data safe.

intermediate

How do you mark a module as server-only in Next.js?

Import `server-only` at the top of the file (e.g., `import 'server-only';`). Place the module where it is used only in server components or server actions.

beginner

Why should you use server-only modules for database access?

Because database credentials and queries should never be exposed to the browser. Server-only modules keep this code hidden and secure on the server.

intermediate

Can server-only modules import client-side code in Next.js?

No, server-only modules cannot import client-side code because client code depends on browser APIs that don't exist on the server.

intermediate

What happens if you try to use server-only modules in client components?

Next.js will throw an error during build or runtime because server-only modules are not allowed in client components to protect security and avoid runtime issues.

What is the main purpose of server-only modules in Next.js?

A To improve client-side rendering speed

B To style components

C To share code between client and server

D To keep sensitive code hidden from the browser

Server-only modules keep sensitive logic like database access hidden from the browser.

Where should you place server-only modules in a Next.js app?

A Inside the 'pages/api' directory only

B Inside the 'public' directory

C Inside the 'app' directory and used only in server components

D Anywhere, no restrictions

Server-only modules belong in the 'app' directory and are used only in server components or server actions.

What do you add at the top of a file to mark it as server-only?

A "use client"

B import "server-only";

C "use strict"

D "use module"

import "server-only"; marks the module as server-only in Next.js and errors if imported into client code.

Can server-only modules import browser APIs like 'window' or 'document'?

A No, because those APIs don't exist on the server

B Yes, always

C Only if you use dynamic imports

D Only in development mode

Browser APIs like 'window' or 'document' are not available on the server, so server-only modules cannot use them.

What error occurs if you import a server-only module inside a client component?

A Build or runtime error preventing the app from running

B Silent failure with no error

C Warning but app still runs

D No error, it works fine

Next.js throws an error to prevent exposing server-only code in client components.

Explain what server-only modules are in Next.js and why they are important.

Think about what code should never be visible to users.

Describe how to create and use a server-only module in a Next.js app.

Focus on file location, directives, and usage rules.