Parallel routes (@slot) in NextJS - Mini Project: Build & Apply

Create Parallel Routes with @slot in Next.js

📖 Scenario: You are building a simple blog website using Next.js. You want to show a sidebar with a list of categories alongside the main content area. The sidebar and main content should be separate routes that render together on the same page using parallel routes and the @slot feature.

🎯 Goal: Build a Next.js app with parallel routes using @slot to display a sidebar of categories and main blog posts side by side.

📋 What You'll Learn

Create a categories array with exact category names

Add a @sidebar parallel route configuration

Use @slot in the layout to render sidebar and main content

Create separate components for sidebar and main content routes

💡 Why This Matters

🌍 Real World

Parallel routes with @slot let you build complex layouts like dashboards, blogs, or admin panels where multiple parts of the page update independently but share the same URL.

💼 Career

Understanding parallel routes and layout composition is essential for building scalable Next.js applications used in professional web development.

1

DATA SETUP: Create the categories array

Create a file app/categories/data.js and inside it create an array called categories with these exact strings: 'Technology', 'Health', 'Travel', 'Finance'.

NextJS

// Your code here

Hint

Remember to export the categories array so other files can use it.

2

CONFIGURATION: Add the sidebar parallel route folder

Inside the app folder, create a folder named @sidebar to be used as a parallel route. This folder will hold the sidebar content component.

NextJS

export const categories = ['Technology', 'Health', 'Travel', 'Finance'];
// Create a folder named '@sidebar' inside 'app' for the parallel route

Hint

Parallel routes in Next.js are created by adding folders inside app with the route name starting with @.

3

CORE LOGIC: Use @slot in the layout to render sidebar and main content

In the app/layout.js file, update the root layout component to include the {@sidebar} slot for the sidebar parallel route and the default {children} slot for main content. Use a flex container to display them side by side.

NextJS

export const categories = ['Technology', 'Health', 'Travel', 'Finance'];

// Folder created: app/@sidebar/

export default function RootLayout({ children }) {
  return (
    
      
        {/* Add flex container with @slot for sidebar and main content here */}
      
    
  );
}

Hint

Use {@sidebar} to render the sidebar parallel route and {children} for the main content.

4

COMPLETION: Create sidebar and main content components

Create app/@sidebar/page.js that imports categories and renders them in a list. Also create app/page.js that shows a heading Welcome to the Blog. These two routes will render side by side using the parallel routes setup.

NextJS

export const categories = ['Technology', 'Health', 'Travel', 'Finance'];

// Folder created: app/@sidebar/

export default function RootLayout({ children }) {
  return (
    
      
        
          
            {@sidebar}
          
          
            {children}
          
        
      
    
  );
}

// Create app/@sidebar/page.js and app/page.js with the described content
// Your code here

Hint

Remember to import categories in app/@sidebar/page.js and map over them to create list items.

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