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.