Multiple root layouts with route groups in NextJS - Performance & Optimization

Performance: Multiple root layouts with route groups

MEDIUM IMPACT

This affects the initial page load speed and rendering performance by controlling how layouts and route groups are loaded and rendered.

Organizing routes with multiple root layouts and route groups to optimize loading

NextJS

app/(marketing)/layout.js
app/(marketing)/page.js
app/(dashboard)/layout.js
app/(dashboard)/page.js

// Using route groups with separate root layouts so only relevant layout code loads per route group.

Separates layout code by route groups, reducing bundle size and speeding up initial render.

📈 Performance GainSaves 50-100ms on LCP by loading smaller layout bundles.

Organizing routes with multiple root layouts and route groups to optimize loading

NextJS

app/layout.js
app/page.js
app/dashboard/layout.js
app/dashboard/page.js
app/settings/layout.js
app/settings/page.js

// All layouts are nested under a single root layout causing all layout code to load on every page.

All layout components load regardless of the route, increasing bundle size and delaying Largest Contentful Paint.

📉 Performance CostBlocks rendering for extra 100-200ms due to unnecessary layout code loading.

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Single root layout for all routes	High (all layouts rendered)	Multiple reflows per page load	High paint cost due to large DOM	[X] Bad
Multiple root layouts with route groups	Low (only relevant layouts rendered)	Single reflow per route group	Lower paint cost with smaller DOM	[OK] Good

Rendering Pipeline

Multiple root layouts with route groups affect how the browser processes and paints the page by controlling which layout components are included in the render tree.

→Style Calculation

→Layout

→Paint

→Composite

⚠️ BottleneckLayout and Paint stages due to larger DOM and CSS from unnecessary layouts.

Core Web Vital Affected

LCP

This affects the initial page load speed and rendering performance by controlling how layouts and route groups are loaded and rendered.

Optimization Tips

1Use route groups to split layouts and reduce bundle size.

2Avoid nesting all routes under a single root layout to prevent loading unused code.

3Smaller layout bundles improve Largest Contentful Paint (LCP) and user experience.

Performance Quiz - 3 Questions

How do multiple root layouts with route groups affect the Largest Contentful Paint (LCP)?

A They reduce LCP by loading only necessary layout code per route group.

B They increase LCP by loading all layouts on every page.

C They have no effect on LCP.

D They delay LCP by adding extra network requests.

DevTools: Performance

How to check: Record a page load and inspect the Main thread for scripting and rendering times; check the Call Tree for layout and paint events.

What to look for: Look for reduced scripting and rendering times, fewer layout and paint events indicating optimized layout usage.

Practice

1. What is the main purpose of using multiple root layouts in a Next.js app?

easy

A. To load all pages with the same layout

B. To change the URL structure automatically

C. To have different main designs for different parts of the app

D. To disable routing in some parts of the app

Solution

1. Step 1: Understand root layouts

   Root layouts define the main design or structure for pages in a Next.js app.

2. Step 2: Purpose of multiple root layouts

   Using multiple root layouts allows different parts of the app to have their own main design, improving organization and user experience.

3. Final Answer:

   To have different main designs for different parts of the app -> Option C

4. Quick Check:

   Multiple root layouts = different main designs [OK]

Hint: Multiple root layouts mean different main designs [OK]

Common Mistakes:

• Thinking multiple root layouts change URLs
• Assuming all pages share one layout
• Believing layouts disable routing

2. Which folder name correctly creates a route group without changing the URL in Next.js?

easy

A. dashboard/(admin)/settings

B. dashboard/admin/settings

C. dashboard/[admin]/settings

D. dashboard/{admin}/settings

Solution

1. Step 1: Identify route group syntax

   Route groups use parentheses in folder names to group routes without affecting URLs.

2. Step 2: Check options

   Only dashboard/(admin)/settings uses parentheses correctly: (admin). Other options use brackets or braces which are for dynamic routes or invalid.

3. Final Answer:

   dashboard/(admin)/settings -> Option A

4. Quick Check:

   Route groups use parentheses ( ) [OK]

Hint: Route groups use ( ) in folder names [OK]

Common Mistakes:

• Using square brackets [] for route groups
• Using curly braces {} which are invalid
• Confusing dynamic routes with route groups

3. Given this folder structure:

app/
  (marketing)/
    layout.js
    page.js
  (dashboard)/
    layout.js
    dashboard/page.js

What layout will the page at URL / use?

medium

A. Both layouts will be combined

B. The layout from (dashboard) folder

C. No layout will be applied

D. The layout from (marketing) folder

Solution

1. Step 1: Understand route groups and root layouts

   Route groups like (marketing) and (dashboard) separate parts of the app with their own layouts.

2. Step 2: Determine which route group matches URL '/'

   The root URL '/' matches the (marketing) group because it is the default or main group for the homepage.

3. Final Answer:

   The layout from (marketing) folder -> Option D

4. Quick Check:

   URL '/' uses (marketing) layout [OK]

Hint: Root URL uses main route group's layout [OK]

Common Mistakes:

• Assuming dashboard layout applies to '/'
• Thinking layouts combine automatically
• Believing no layout applies by default

4. You created a route group folder named (admin) but your app shows a 404 error when visiting /admin. What is the likely mistake?

medium

A. You forgot to restart the Next.js server

B. Route group folders do not change URLs, so /admin URL does not exist

C. You must add a dynamic route file inside (admin) folder

D. Parentheses in folder names are invalid syntax

Solution

1. Step 1: Understand route groups and URLs

   Route groups using parentheses group routes but do not add to the URL path.

2. Step 2: Check URL vs folder name

   The folder (admin) does not create /admin URL. To have /admin URL, folder must be named 'admin' without parentheses.

3. Final Answer:

   Route group folders do not change URLs, so /admin URL does not exist -> Option B

4. Quick Check:

   Route groups don't add URL segments [OK]

Hint: Route groups don't add URL parts [OK]

Common Mistakes:

• Thinking (admin) folder creates /admin URL
• Believing parentheses are invalid
• Assuming dynamic routes are needed here

5. You want to create two separate main layouts: one for public pages and one for user dashboard pages. You also want URLs like /login and /dashboard/profile. How should you organize your folders using multiple root layouts and route groups?

hard

A. Create app/(public)/layout.js and app/(dashboard)/layout.js, put pages inside each, and use route groups to keep URLs clean

B. Create app/public/layout.js and app/dashboard/layout.js folders without parentheses

C. Put all pages in app/layout.js and use conditional rendering inside layout

D. Use dynamic routes like app/[section]/layout.js to switch layouts

Solution

1. Step 1: Use route groups for separate layouts

   Route groups with parentheses let you organize folders without affecting URLs, perfect for multiple root layouts.

2. Step 2: Organize folders for public and dashboard

   Creating (public) and (dashboard) folders with their own layouts keeps code clean and URLs like /login and /dashboard/profile work as expected.

3. Final Answer:

   Create app/(public)/layout.js and app/(dashboard)/layout.js, put pages inside each, and use route groups to keep URLs clean -> Option A

4. Quick Check:

   Route groups + multiple root layouts = clean URLs and separate designs [OK]

Hint: Use ( ) folders for layouts without changing URLs [OK]

Common Mistakes:

• Not using parentheses, causing URL changes
• Putting all pages under one layout losing separation
• Using dynamic routes incorrectly for layouts