How Next.js renders (server-first model) - Performance Optimization Steps

Performance: How Next.js renders (server-first model)

HIGH IMPACT

This affects the initial page load speed and time to first meaningful paint by rendering content on the server before sending it to the browser.

Rendering a page with dynamic content

NextJS

export const dynamic = 'force-static';

async function Page() {
  const data = await fetch('https://api.example.com/data').then(res => res.json());
  return <div>{data.message}</div>;
}

export default Page;

Fetching data on the server before sending HTML allows immediate content display, improving LCP and perceived speed.

📈 Performance GainReduces LCP by up to 2 seconds and avoids blocking on client JS execution.

Rendering a page with dynamic content

NextJS

import React from 'react';

export default function Page() {
  const [data, setData] = React.useState(null);
  React.useEffect(() => {
    fetch('/api/data').then(res => res.json()).then(setData);
  }, []);
  if (!data) return <p>Loading...</p>;
  return <div>{data.message}</div>;
}

This client-side fetching delays content rendering until JavaScript runs, causing slower initial paint and worse LCP.

📉 Performance CostBlocks meaningful content rendering until JS loads and runs, increasing LCP by 1-2 seconds on slow networks.

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Client-side data fetching after load	Many (dynamic nodes created after JS runs)	Multiple reflows as content loads	High paint cost due to delayed content	[X] Bad
Server-first rendering with pre-fetched data	Minimal (static HTML nodes)	Single reflow on initial paint	Low paint cost with immediate content	[OK] Good

Rendering Pipeline

Next.js server-first rendering sends fully rendered HTML to the browser, reducing client-side work. The browser can paint content immediately without waiting for JavaScript to fetch or render data.

→HTML Generation

→Network Transfer

→Initial Paint

⚠️ BottleneckNetwork Transfer and Server Rendering time

Core Web Vital Affected

LCP

This affects the initial page load speed and time to first meaningful paint by rendering content on the server before sending it to the browser.

Optimization Tips

1Render pages on the server to send ready HTML for faster initial paint.

2Avoid fetching data only on the client to prevent delayed content rendering.

3Use caching and incremental static regeneration to speed up server response times.

Performance Quiz - 3 Questions

What is the main performance benefit of Next.js server-first rendering?

A Smaller JavaScript bundle size

B Faster initial content display by sending pre-rendered HTML

C Reduced CSS file size

D Improved client-side interactivity speed

DevTools: Performance

How to check: Record a page load in the Performance panel. Look for the time when the main content is painted and when JavaScript execution starts.

What to look for: A shorter time to first meaningful paint and less blocking time before content appears indicates good server-first rendering.

Practice

1. What is the main reason Next.js renders pages on the server first?

easy

A. To avoid using React components

B. To run JavaScript only on the client

C. To improve page load speed and SEO

D. To prevent any HTML from being sent to the browser

Solution

1. Step 1: Understand server-first rendering purpose

   Next.js renders pages on the server to send fully formed HTML to the browser quickly.

2. Step 2: Connect server rendering to SEO and speed

   Sending ready HTML helps search engines read content and users see pages faster.

3. Final Answer:

   To improve page load speed and SEO -> Option C

4. Quick Check:

   Server-first rendering = better speed and SEO [OK]

Hint: Server rendering means faster pages and better SEO [OK]

Common Mistakes:

• Thinking server rendering delays page load
• Believing React is not used in Next.js
• Assuming HTML is not sent to the browser

2. Which Next.js function is used to fetch data on the server before rendering a page?

easy

A. getServerSideProps

B. componentDidMount

C. useEffect

D. getStaticProps

Solution

1. Step 1: Identify server-side data fetching functions

   Next.js provides getServerSideProps to fetch data on the server at request time.

2. Step 2: Differentiate from other functions

   getStaticProps runs at build time, useEffect and componentDidMount run on client side.

3. Final Answer:

   getServerSideProps -> Option A

4. Quick Check:

   Server data fetch = getServerSideProps [OK]

Hint: Server data fetch uses getServerSideProps [OK]

Common Mistakes:

• Confusing getStaticProps with server-side fetching
• Using client hooks like useEffect for server data
• Thinking componentDidMount runs on server

3. Given this Next.js page code, what will the browser initially receive?

export async function getServerSideProps() {
  return { props: { message: 'Hello from server' } };
}

export default function Page({ message }) {
  return <h1>{message}</h1>;
}

medium

A. HTML with <h1>Hello from server</h1>

B. An empty page with no content

C. JavaScript code only, no HTML

D. A JSON object with the message

Solution

1. Step 1: Understand getServerSideProps role

   This function runs on the server and passes props to the component before rendering.

2. Step 2: Determine what is sent to browser

   The browser receives fully rendered HTML with the message inside an <h1> tag.

3. Final Answer:

   HTML with <h1>Hello from server</h1> -> Option A

4. Quick Check:

   Server props produce HTML output [OK]

Hint: Server props render HTML sent to browser first [OK]

Common Mistakes:

• Expecting raw JavaScript or JSON instead of HTML
• Thinking page is empty initially
• Confusing client-side rendering with server rendering

4. What is wrong with this Next.js page code?

export async function getServerSideProps() {
  const data = await fetch('https://api.example.com/data');
  return { props: { data } };
}

export default function Page({ data }) {
  return <div>{data.title}</div>;
}

medium

A. React components cannot use props

B. getServerSideProps cannot be async

C. Props cannot be passed to components

D. fetch returns a Response object, not JSON data

Solution

1. Step 1: Check fetch usage in getServerSideProps

   fetch returns a Response object; to get JSON, .json() must be called.

2. Step 2: Identify missing JSON parsing

   Without calling await data.json(), data is not the actual JSON, causing errors in rendering.

3. Final Answer:

   fetch returns a Response object, not JSON data -> Option D

4. Quick Check:

   fetch needs .json() to get data [OK]

Hint: Always parse fetch response with .json() in server props [OK]

Common Mistakes:

• Assuming fetch returns JSON directly
• Thinking getServerSideProps can't be async
• Believing props can't be passed to components

5. You want to render a page that shows a list of users fetched from an API on every request. Which Next.js approach correctly ensures the page is server-rendered with fresh data each time?

hard

A. Use getStaticProps to fetch users at build time

B. Use getServerSideProps to fetch users on each request

C. Fetch users inside useEffect in the component

D. Hardcode the user list in the component

Solution

1. Step 1: Understand data freshness needs

   Fetching fresh data on every request requires server-side fetching at request time.

2. Step 2: Match Next.js data fetching methods

   getServerSideProps runs on each request, while getStaticProps runs once at build time.

3. Step 3: Evaluate client-side fetching

   Fetching inside useEffect delays data until after page load, hurting SEO and initial render.

4. Final Answer:

   Use getServerSideProps to fetch users on each request -> Option B

5. Quick Check:

   Fresh server data = getServerSideProps [OK]

Hint: Fresh data each request? Use getServerSideProps [OK]

Common Mistakes:

• Using getStaticProps for dynamic data
• Fetching data only on client side
• Hardcoding data instead of fetching