Parallel routes (@slot) in NextJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of parallel routes in Next.js using @slot?

Parallel routes let you show different parts of the UI at the same time, like sidebars or modals, without replacing the main page content. The <code>@slot</code> syntax marks where these extra routes appear.

intermediate

How do you define a parallel route in Next.js app router?

You create a folder with the route name inside parentheses, like @sidebar, and inside it, add a page.tsx. Then in the main layout, use {@sidebar} to show it.

beginner

What does the @slot syntax do in Next.js layouts?

It tells Next.js where to render the content of a parallel route. It acts like a placeholder for that route's UI inside the main layout.

intermediate

Can parallel routes update independently without reloading the main page in Next.js?

Yes! Parallel routes let parts of the UI update separately, so you can change a sidebar or modal without reloading the whole page.

intermediate

Why might you use parallel routes instead of nested routes in Next.js?

Parallel routes let you show multiple UI sections side-by-side or overlayed, like a sidebar and main content, without forcing one inside the other. Nested routes replace or nest content, but parallel routes run alongside.

In Next.js, what does the @slot syntax specify?

A The data fetching method

B Where to render a parallel route's content

C The CSS class for styling

D The URL path of a route

@slot marks the placeholder in a layout where the parallel route's UI will appear.

How do you name a folder to create a parallel route in Next.js app router?

A With parentheses, like (sidebar)

B With square brackets, like [sidebar]

C With curly braces, like {sidebar}

D With angle brackets, like <sidebar>

Parallel route folders use parentheses to separate them from normal routes.

What happens if you omit @slot in a layout for a parallel route?

A The route renders twice

B The app crashes

C The route becomes the main route

D The parallel route content won't render in that layout

Without @slot, Next.js doesn't know where to show the parallel route's UI.

Which UI pattern is best suited for parallel routes in Next.js?

A Single full-page form

B Simple page navigation

C Sidebar or modal alongside main content

D Static content only

Parallel routes let you show multiple UI parts side-by-side or overlayed, like sidebars or modals.

Can parallel routes in Next.js update independently without reloading the whole page?

A Yes, they update separately

B No, they reload the entire page

C Only if using server components

D Only with client-side routing

Parallel routes allow independent UI updates without full page reloads.

Explain how parallel routes work in Next.js and the role of the @slot syntax.

Think about showing a sidebar and main content together.

Describe a real-life example where using parallel routes with @slot in Next.js improves user experience.

Imagine a shopping site with filters on the side.

Practice

1. What is the main purpose of using @slot in Next.js parallel routes?

easy

A. To display multiple UI parts simultaneously in different route segments

B. To fetch data from an API endpoint

C. To define server-side rendering behavior

D. To create dynamic API routes

Solution

1. Step 1: Understand the role of @slot

   @slot is used to show multiple UI parts at once by matching route segments.

2. Step 2: Identify the purpose in parallel routes

   It allows different UI sections to render in parallel, improving layout flexibility.

3. Final Answer:

   To display multiple UI parts simultaneously in different route segments -> Option A

4. Quick Check:

   Parallel routes use @slot to show multiple UI parts [OK]

Hint: Remember: @slot shows multiple UI parts at once [OK]

Common Mistakes:

• Confusing @slot with data fetching
• Thinking @slot controls API routes
• Assuming @slot is for server rendering only

2. Which of the following is the correct syntax to define a parallel route slot named sidebar in Next.js?

easy

A. export const @slot sidebar = () => <div>Sidebar</div>;

B. export const slot_sidebar = () => <div>Sidebar</div>;

C. export const sidebar = () => <div>Sidebar</div>;

D. export const SidebarSlot = () => <div>Sidebar</div>;

Solution

1. Step 1: Recall parallel route slot syntax

   Slots are exported as named exports matching the slot name, e.g., export const sidebar.

2. Step 2: Check each option

   export const sidebar = () => <div>Sidebar</div>; correctly exports a constant named sidebar as a React component.

3. Final Answer:

   export const sidebar = () => <div>Sidebar</div>; -> Option C

4. Quick Check:

   Slot name matches export const name [OK]

Hint: Export slot as named const matching slot name [OK]

Common Mistakes:

• Using @slot keyword in export
• Prefixing slot name incorrectly
• Using PascalCase instead of slot name

3. Given this Next.js parallel route layout code:

export const header = () => <header>Header</header>;
export const footer = () => <footer>Footer</footer>;

export default function Page() {
  return <main>Main Content</main>;
}

What will be rendered on the page?

medium

A. Only <main>Main Content</main> is rendered

B. <header>Header</header>, <main>Main Content</main>, and <footer>Footer</footer> are all rendered

C. Only <header>Header</header> and <footer>Footer</footer> are rendered

D. Syntax error due to missing @slot usage

Solution

1. Step 1: Understand parallel route slots rendering

   Slots like header and footer render alongside the default export component.

2. Step 2: Combine all parts

   The page renders header, main content, and footer together as parallel UI parts.

3. Final Answer:

   <header>Header</header>, <main>Main Content</main>, and <footer>Footer</footer> are all rendered -> Option B

4. Quick Check:

   Parallel routes render all slots plus default [OK]

Hint: Slots and default export render together [OK]

Common Mistakes:

• Thinking only default export renders
• Assuming slots need explicit @slot tags in JSX
• Confusing syntax error with missing @slot

4. You wrote this code for a parallel route slot:

export const sidebar = () => <div>Sidebar</div>;

export default function Page() {
  return <main>Main</main>;
}

But the sidebar does not appear on the page. What is the likely cause?

medium

A. The slot name sidebar does not match any route segment

B. You forgot to import React

C. The default export must be named sidebar

D. Parallel routes require class components, not functions

Solution

1. Step 1: Check slot name and route segment matching

   Slots render only if their name matches a parallel route segment in the folder structure.

2. Step 2: Identify mismatch issue

   If no route segment named sidebar exists, the slot won't render.

3. Final Answer:

   The slot name sidebar does not match any route segment -> Option A

4. Quick Check:

   Slot name must match route segment [OK]

Hint: Match slot name exactly to route segment folder [OK]

Common Mistakes:

• Assuming React import is required in Next.js 13+
• Thinking default export must be slot named
• Believing only class components work for slots

5. You want to create a layout with parallel routes showing a nav bar and a content area side by side. Which folder structure and code setup correctly implements this using @slot?

hard

A. Folders: app/(nav)/page.tsx and app/(content)/page.tsx with export const nav = () => <nav>Nav</nav>; in nav folder and export default function Page() { return <main>Content</main>; } in content folder

B. Folders: app/(nav)/page.tsx and app/(content)/page.tsx with export default function Nav() { return <nav>Nav</nav>; } and export default function Content() { return <main>Content</main>; }

C. Folders: app/nav/page.tsx and app/content/page.tsx with export default function Nav() { return <nav>Nav</nav>; } and export default function Content() { return <main>Content</main>; }

D. Folders: app/nav/page.tsx and app/content/page.tsx with export const nav = () => <nav>Nav</nav>; in nav folder and export default function Page() { return <main>Content</main>; } in content folder

Solution

1. Step 1: Understand parallel route folder naming

   Parallel routes use folder names without parentheses to define slots, e.g., nav and content.

2. Step 2: Match slot export and default export

   In nav folder, export export const nav for the slot; in content folder, export default the main content.

3. Step 3: Verify options

   Folders: app/nav/page.tsx and app/content/page.tsx with export const nav = () => <nav>Nav</nav>; in nav folder and export default function Page() { return <main>Content</main>; } in content folder correctly uses folders app/nav and app/content with proper exports.

4. Final Answer:

   Folders: app/nav/page.tsx and app/content/page.tsx with export const nav and default export in content -> Option D

5. Quick Check:

   Folder names match slot names without parentheses [OK]

Hint: Use folder names matching slot names without parentheses [OK]

Common Mistakes:

• Using parentheses in folder names for slots
• Exporting slots as default exports
• Mixing slot export and default export roles