Route prefetching behavior in NextJS - Performance & Optimization

Performance: Route prefetching behavior

MEDIUM IMPACT

Route prefetching affects page load speed by loading page code and data before the user navigates, improving perceived navigation speed.

Prefetching routes in a Next.js app to improve navigation speed

NextJS

import Link from 'next/link';

export default function Nav() {
  return (
    <nav>
      <Link href="/about">About</Link>
      <Link href="/contact">Contact</Link>
      <Link href="/products">Products</Link>
    </nav>
  );
}

Next.js automatically prefetches routes only when links enter the viewport and user likely to navigate, reducing wasted requests and improving LCP.

📈 Performance GainPrefetches fewer routes on demand, reducing blocking and saving bandwidth.

Prefetching routes in a Next.js app to improve navigation speed

NextJS

import Link from 'next/link';

export default function Nav() {
  return (
    <nav>
      <Link href="/about" prefetch={true}>About</Link>
      <Link href="/contact" prefetch={true}>Contact</Link>
      <Link href="/products" prefetch={true}>Products</Link>
    </nav>
  );
}

Prefetching all routes immediately on page load wastes bandwidth and CPU, delaying main content rendering and increasing data usage.

📉 Performance CostTriggers multiple network requests upfront, blocking LCP and increasing data usage unnecessarily.

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Eager prefetch all links	Minimal	0	Increased due to delayed main content	[X] Bad
Automatic viewport-based prefetch	Minimal	0	Minimal paint delay, faster navigation	[OK] Good

Rendering Pipeline

Route prefetching initiates network requests for JavaScript bundles and data before navigation. This affects the browser's loading and scripting stages, potentially delaying main content if overused.

→Network

→Script Evaluation

→Layout

⚠️ BottleneckNetwork requests triggered too early can block main content loading and script execution.

Core Web Vital Affected

LCP

Route prefetching affects page load speed by loading page code and data before the user navigates, improving perceived navigation speed.

Optimization Tips

1Avoid prefetching all routes immediately to prevent blocking main content.

2Let Next.js prefetch routes only when links are visible to save bandwidth.

3Monitor network requests to ensure prefetching does not overload the connection.

Performance Quiz - 3 Questions

What is the main performance risk of prefetching all routes immediately on page load in Next.js?

A It wastes bandwidth and delays main content rendering.

B It causes layout shifts during navigation.

C It blocks user input responsiveness.

D It increases CSS selector complexity.

DevTools: Network

How to check: Open DevTools, go to Network tab, reload page, and observe prefetch requests for route chunks. Check if many requests fire immediately or only on scroll/hover.

What to look for: Look for many JS chunk requests firing upfront (bad) versus requests triggered only when links appear in viewport (good).

Practice

1. What is the main purpose of route prefetching in Next.js?

easy

A. To prevent users from navigating to certain pages

B. To disable client-side navigation

C. To load pages in the background before the user navigates to them

D. To increase the size of the initial JavaScript bundle

Solution

1. Step 1: Understand what prefetching means

   Prefetching means loading resources ahead of time before they are needed.

2. Step 2: Apply this to Next.js routing

   Next.js prefetches pages in the background to make navigation faster when the user clicks a link.

3. Final Answer:

   To load pages in the background before the user navigates to them -> Option C

4. Quick Check:

   Prefetching = background loading [OK]

Hint: Prefetching means loading before navigation happens [OK]

Common Mistakes:

• Thinking prefetching blocks navigation
• Confusing prefetching with disabling navigation
• Assuming prefetching increases initial load size

2. Which of the following is the correct way to disable automatic prefetching on a Next.js Link component?

easy

A. <Link href='/about' prefetch={false}>About</Link>

B. <Link href='/about' prefetch>About</Link>

C. <Link href='/about' noPrefetch>About</Link>

D. <Link href='/about' prefetch='off'>About</Link>

Solution

1. Step 1: Recall the prefetch prop usage

   The prefetch prop accepts a boolean to enable or disable prefetching.

2. Step 2: Identify the correct syntax to disable prefetching

   Setting prefetch={false} disables automatic prefetching on the Link.

3. Final Answer:

   <Link href='/about' prefetch={false}>About</Link> -> Option A

4. Quick Check:

   Disable prefetch with prefetch={false} [OK]

Hint: Use prefetch={false} to turn off prefetching [OK]

Common Mistakes:

• Using just 'prefetch' without value disables prefetching
• Using non-existent props like noPrefetch
• Passing string values instead of boolean

3. Consider this Next.js code snippet:

import Link from 'next/link';

export default function Home() {
  return (
    <div>
      <Link href='/profile' prefetch>Go to Profile</Link>
    </div>
  );
}

What happens when this component renders in the browser?

medium

A. The '/profile' page is not prefetched because prefetch defaults to false

B. The '/profile' page is prefetched in the background to speed up navigation

C. The link will cause a full page reload when clicked

D. The component will throw a syntax error due to incorrect prefetch usage

Solution

1. Step 1: Check the prefetch prop usage

   The prefetch prop is present without a value, which means it is true.

2. Step 2: Understand Next.js default behavior

   Next.js prefetches linked pages by default, so explicitly adding prefetch confirms this behavior.

3. Final Answer:

   The '/profile' page is prefetched in the background to speed up navigation -> Option B

4. Quick Check:

   prefetch present = prefetch enabled [OK]

Hint: Presence of prefetch prop means prefetching is on [OK]

Common Mistakes:

• Thinking prefetch defaults to false
• Assuming link causes full page reload
• Confusing syntax with errors

4. You wrote this code to prefetch a route manually:

import { useRouter } from 'next/router';
import { useEffect } from 'react';

export default function Page() {
  const router = useRouter();

  useEffect(() => {
    router.prefetch('/dashboard');
  }, []);

  return <div>Welcome</div>;
}

However, the prefetch does not seem to work. What is the likely cause?

medium

A. You must call router.prefetch inside an event handler, not useEffect

B. The router.prefetch method does not exist in Next.js

C. The router.prefetch method is asynchronous and needs to be awaited

D. The useRouter import path is incorrect; it should be from 'next/navigation'

Solution

1. Step 1: Check the import source of useRouter

   In Next.js 14+, useRouter for client navigation is imported from 'next/navigation', not 'next/router'.

2. Step 2: Understand impact on router.prefetch

   Importing from 'next/router' gives an outdated router without prefetch support, so prefetch won't work.

3. Final Answer:

   The useRouter import path is incorrect; it should be from 'next/navigation' -> Option D

4. Quick Check:

   Correct import = 'next/navigation' [OK]

Hint: Use 'next/navigation' for router.prefetch in Next.js 14+ [OK]

Common Mistakes:

• Importing useRouter from 'next/router' instead of 'next/navigation'
• Not awaiting async prefetch (not required)
• Thinking prefetch only works in event handlers

5. You want to optimize bandwidth by prefetching only when a user hovers over a link. Which approach correctly implements this in Next.js?

hard

A. Set prefetch={false} on Link and call router.prefetch() inside an onMouseEnter event handler

B. Set prefetch on Link and call router.prefetch() inside useEffect

C. Remove prefetch from Link and rely on default prefetching

D. Use prefetch={true} on Link and disable prefetching globally in config

Solution

1. Step 1: Disable automatic prefetching on the Link

   Set prefetch={false} to prevent Next.js from prefetching immediately.

2. Step 2: Prefetch manually on user hover

   Use onMouseEnter event to call router.prefetch() to load the page only when user shows interest.

3. Final Answer:

   Set prefetch={false} on Link and call router.prefetch() inside an onMouseEnter event handler -> Option A

4. Quick Check:

   Manual prefetch on hover = prefetch={false} + onMouseEnter [OK]

Hint: Disable auto prefetch, prefetch manually on hover event [OK]

Common Mistakes:

• Prefetching both automatically and manually causing wasted bandwidth
• Calling prefetch in useEffect instead of on hover
• Relying on default prefetching without control