What is Next.js - Performance Impact

Performance: What is Next.js

MEDIUM IMPACT

Next.js affects page load speed and rendering performance by optimizing server-side rendering and static generation.

Rendering a React app with fast initial load

NextJS

import React from 'react';

export default function Page() {
  return <div>Hello World</div>;
}

// Next.js pre-renders this page on server or at build time

Pre-rendering sends fully rendered HTML to browser, speeding up first meaningful paint.

📈 Performance GainImproves LCP by reducing time to first contentful paint

Rendering a React app with fast initial load

NextJS

import React from 'react';

export default function App() {
  return <div>Hello World</div>;
}

// Rendered only on client side

Client-side rendering delays content display until JavaScript loads and runs.

📉 Performance CostBlocks LCP until JS is downloaded and parsed

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Client-side React only	Many on client after JS loads	Multiple reflows during hydration	High paint cost due to delayed content	[X] Bad
Next.js pre-rendered page	Minimal on client at load	Single reflow on initial paint	Low paint cost with fast content display	[OK] Good

Rendering Pipeline

Next.js pre-renders pages on the server or at build time, sending ready HTML to the browser. This reduces the time spent in JavaScript execution and layout calculation on the client.

→HTML Parsing

→Style Calculation

→Layout

→Paint

⚠️ BottleneckJavaScript execution and hydration on client

Core Web Vital Affected

LCP

Next.js affects page load speed and rendering performance by optimizing server-side rendering and static generation.

Optimization Tips

1Pre-render pages to reduce client JavaScript and speed up initial paint.

2Use static generation for pages that don’t change often to improve load times.

3Server-side rendering helps deliver fresh content without slowing down the user experience.

Performance Quiz - 3 Questions

How does Next.js improve page load speed compared to client-only React?

A By loading all JavaScript before showing any content

B By pre-rendering pages on the server or at build time

C By delaying rendering until user interaction

D By removing CSS from the page

DevTools: Performance

How to check: Record page load and look for time to first contentful paint and scripting time.

What to look for: Short time to first contentful paint and low scripting time indicate good Next.js performance.

Practice

1. What is Next.js primarily used for?

easy

A. Writing backend server code without frontend

B. Creating mobile apps with native device access

C. Designing databases for web applications

D. Building React-based websites with routing and performance features

Solution

1. Step 1: Understand Next.js purpose

   Next.js is a framework built on top of React to simplify building websites.

2. Step 2: Identify key features

   It adds routing, faster loading, and SEO support to React apps.

3. Final Answer:

   Building React-based websites with routing and performance features -> Option D

4. Quick Check:

   Next.js = React websites + routing + speed [OK]

Hint: Next.js helps build React websites easily [OK]

Common Mistakes:

• Confusing Next.js with mobile app frameworks
• Thinking Next.js is only backend
• Assuming Next.js is a database tool

2. Which of the following is the correct way to create a page in Next.js?

easy

A. Write HTML files in the public folder

B. Add routes manually in a routing config file

C. Create a React component inside the pages folder

D. Use index.html in the root directory

Solution

1. Step 1: Recall Next.js page creation method

   Next.js uses the pages folder where each file is a React component representing a page.

2. Step 2: Compare options

   Only Create a React component inside the pages folder matches this pattern; others describe static or manual routing methods not used in Next.js.

3. Final Answer:

   Create a React component inside the pages folder -> Option C

4. Quick Check:

   Next.js pages = React components in pages folder [OK]

Hint: Pages are React components in the pages folder [OK]

Common Mistakes:

• Thinking HTML files in public folder create pages
• Believing manual routing config is needed
• Using index.html instead of React components

3. What will Next.js do when you create a file about.js inside the pages folder?

medium

A. Serve the page at URL /about automatically

B. Require manual route setup to access /about

C. Ignore the file unless imported elsewhere

D. Throw an error because pages must be in src folder

Solution

1. Step 1: Understand Next.js file-based routing

   Next.js automatically maps files in pages folder to URLs matching the filename.

2. Step 2: Apply to about.js

   The file about.js becomes accessible at /about without extra setup.

3. Final Answer:

   Serve the page at URL /about automatically -> Option A

4. Quick Check:

   File in pages = URL path [OK]

Hint: File name in pages = URL path automatically [OK]

Common Mistakes:

• Thinking manual routing is needed
• Assuming files outside src are required
• Believing files are ignored if not imported

4. You wrote a React component in pages/contact.js but visiting /contact shows a 404 error. What is the likely mistake?

medium

A. The file is placed inside public folder

B. The component is not exported as default

C. Next.js requires manual route registration

D. The file name must be Contact.jsx with uppercase

Solution

1. Step 1: Check Next.js page export rules

   Each page component must be the default export from its file to be recognized.

2. Step 2: Analyze error cause

   If the component is not exported as default, Next.js won't load it, causing 404.

3. Final Answer:

   The component is not exported as default -> Option B

4. Quick Check:

   Pages need default export [OK]

Hint: Always export page component as default [OK]

Common Mistakes:

• Placing pages in public folder instead of pages
• Thinking manual route setup is needed
• Using uppercase file names incorrectly

5. You want to improve SEO and loading speed of your React website. How does Next.js help achieve this?

hard

A. By pre-rendering pages on the server and generating static HTML

B. By running React code only on the client side after page load

C. By disabling JavaScript to speed up loading

D. By converting React components into plain HTML files manually

Solution

1. Step 1: Understand Next.js rendering methods

   Next.js pre-renders pages either at build time or on the server, creating static or server-rendered HTML.

2. Step 2: Connect to SEO and speed benefits

   Pre-rendered HTML loads faster and is better for search engines than client-only React apps.

3. Final Answer:

   By pre-rendering pages on the server and generating static HTML -> Option A

4. Quick Check:

   Next.js pre-renders for SEO and speed [OK]

Hint: Next.js pre-renders pages for SEO and speed [OK]

Common Mistakes:

• Thinking React runs only on client in Next.js
• Believing JavaScript must be disabled
• Assuming manual HTML conversion is needed