Why server components are the default in NextJS - Performance Evidence

Performance: Why server components are the default

HIGH IMPACT

This affects the initial page load speed and reduces client-side JavaScript execution, improving user experience.

Rendering UI components efficiently in Next.js

NextJS

export default async function Page() {
  const data = await fetchData();
  return <div>Data: {data.value}</div>;
}

This server component renders HTML on the server, sending minimal JS to the client and speeding up load.

📈 Performance GainSaves 50-100kb client bundle, reduces blocking time, improves LCP by 200-500ms

Rendering UI components efficiently in Next.js

NextJS

'use client'

import React from 'react';

export default function Page() {
  const [count, setCount] = React.useState(0);
  return <button onClick={() => setCount(count + 1)}>Count: {count}</button>;
}

This client component sends all React code to the browser, increasing bundle size and delaying initial paint.

📉 Performance CostAdds 50-100kb to client bundle, blocking rendering until JS loads and executes

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Client Components by default	More DOM nodes from hydration	Multiple reflows during hydration	Higher paint cost due to JS execution	[X] Bad
Server Components by default	Minimal DOM nodes, static HTML	Single reflow on initial load	Lower paint cost, faster display	[OK] Good

Rendering Pipeline

Server components render HTML on the server, so the browser receives ready-to-display content without waiting for JS to load. This reduces work in Style Calculation, Layout, and Paint stages on the client.

→HTML Parsing

→Style Calculation

→Layout

→Paint

⚠️ BottleneckClient-side JavaScript execution and hydration

Core Web Vital Affected

LCP

This affects the initial page load speed and reduces client-side JavaScript execution, improving user experience.

Optimization Tips

1Use server components to reduce client JavaScript bundle size.

2Server components speed up initial content display by sending pre-rendered HTML.

3Avoid unnecessary client components to minimize hydration and reflow costs.

Performance Quiz - 3 Questions

Why do server components improve Largest Contentful Paint (LCP) in Next.js?

A They send pre-rendered HTML to the browser, reducing client JS work.

B They increase client-side JavaScript bundle size.

C They delay rendering until all client scripts load.

D They require more reflows during hydration.

DevTools: Performance

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

What to look for: Lower scripting time and faster Largest Contentful Paint indicate good server component usage.