Shallow routing concept in NextJS - Performance & Optimization

Performance: Shallow routing concept

MEDIUM IMPACT

Shallow routing affects page navigation speed by updating the URL without a full page reload or data fetching, improving user experience during route changes.

Navigating between pages while preserving state and avoiding full reloads

NextJS

import { useRouter } from 'next/router';

const router = useRouter();

// Navigating with shallow routing
router.push('/about', undefined, { shallow: true });

Updates URL and component state without full reload or data fetching, resulting in faster navigation and smoother interaction.

📈 Performance GainReduces blocking time to under 50ms and avoids full reflow

Navigating between pages while preserving state and avoiding full reloads

NextJS

import { useRouter } from 'next/router';

const router = useRouter();

// Navigating with full reload
router.push('/about');

Triggers a full page reload and data fetching, causing slower navigation and higher input delay.

📉 Performance CostBlocks rendering for 100-300ms depending on data fetching and triggers full reflow

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Full page navigation	Many DOM updates due to reload	Multiple reflows triggered	High paint cost due to full reload	[X] Bad
Shallow routing	Minimal DOM updates, URL change only	Single reflow or none	Low paint cost, smooth transition	[OK] Good

Rendering Pipeline

Shallow routing updates the browser URL and React component state without triggering Next.js data fetching or a full page reload, minimizing work in the rendering pipeline.

→JavaScript Execution

→React Reconciliation

→Paint

→Composite

⚠️ BottleneckJavaScript Execution and React Reconciliation when full reload occurs

Core Web Vital Affected

INP

Shallow routing affects page navigation speed by updating the URL without a full page reload or data fetching, improving user experience during route changes.

Optimization Tips

1Use shallow routing to update URLs without full page reloads.

2Avoid unnecessary data fetching by enabling shallow routing when state is preserved.

3Monitor interaction delays to confirm shallow routing improves responsiveness.

Performance Quiz - 3 Questions

What is the main performance benefit of using shallow routing in Next.js?

A It preloads all page data in advance.

B It disables JavaScript on the page.

C It updates the URL without triggering a full page reload or data fetching.

D It forces a full page reload to refresh content.

DevTools: Performance

How to check: Record a navigation event in the Performance panel. Compare full page reload vs shallow routing by looking at scripting and rendering times.

What to look for: Look for reduced scripting time and fewer layout shifts during shallow routing compared to full reload.

Practice

1. What does shallow routing in Next.js primarily do?

easy

A. Reloads the entire page to fetch new data

B. Prevents URL changes when navigating

C. Changes the URL without reloading the page or losing component state

D. Forces a full server-side render on every navigation

Solution

1. Step 1: Understand shallow routing purpose

   Shallow routing updates the URL but keeps the current page component and state intact without a full reload.

2. Step 2: Compare options with shallow routing behavior

   Only Changes the URL without reloading the page or losing component state describes changing the URL without reloading or losing state, matching shallow routing.

3. Final Answer:

   Changes the URL without reloading the page or losing component state -> Option C

4. Quick Check:

   Shallow routing = URL change without reload [OK]

Hint: Shallow routing changes URL but keeps page state [OK]

Common Mistakes:

• Thinking shallow routing reloads the page
• Assuming shallow routing blocks URL changes
• Confusing shallow routing with full page reload

2. Which is the correct way to enable shallow routing using Next.js router's push method?

easy

A. router.push('/page?tab=1', undefined, { shallow: true })

B. router.push('/page?tab=1', { shallow: true })

C. router.push('/page?tab=1', true)

D. router.push('/page?tab=1', { reload: false })

Solution

1. Step 1: Recall router.push syntax for shallow routing

   The third argument to router.push is an options object where shallow: true enables shallow routing.

2. Step 2: Match options with correct syntax

   router.push('/page?tab=1', undefined, { shallow: true }) correctly passes { shallow: true } as the third argument; others are incorrect or incomplete.

3. Final Answer:

   router.push('/page?tab=1', undefined, { shallow: true }) -> Option A

4. Quick Check:

   Shallow routing option is third argument object [OK]

Hint: Use third argument { shallow: true } in router.push [OK]

Common Mistakes:

• Passing shallow option as second argument
• Using boolean instead of options object
• Confusing reload option with shallow

3. Given this code snippet in a Next.js page component:

const router = useRouter();

useEffect(() => {
  console.log('Query changed:', router.query.tab);
}, [router.query.tab]);

const changeTab = () => {
  router.push('/dashboard?tab=2', undefined, { shallow: true });
};

changeTab();

What will be logged to the console after changeTab() is called?

medium

A. Query changed: 2

B. Query changed: undefined

C. Nothing is logged because shallow routing blocks query updates

D. An error occurs because shallow routing cannot update query

Solution

1. Step 1: Understand effect dependency on router.query.tab

   The effect runs when router.query.tab changes, logging its value.

2. Step 2: Analyze shallow routing effect on query

   Shallow routing updates the URL and query parameters without full reload, so router.query.tab updates to '2'.

3. Final Answer:

   Query changed: 2 -> Option A

4. Quick Check:

   Shallow routing updates query and triggers effects [OK]

Hint: Shallow routing updates query, triggers effects [OK]

Common Mistakes:

• Assuming shallow routing blocks query updates
• Expecting no console output
• Thinking shallow routing causes errors

4. Consider this Next.js code snippet:

const router = useRouter();

const handleClick = () => {
  router.push('/profile?section=info', undefined, { shallow: true });
  router.push('/profile?section=details');
};

handleClick();

What is the problem with this code regarding shallow routing?

medium

A. No problem; shallow routing applies to both pushes automatically

B. Shallow routing is ignored because it must be the first push

C. Both pushes cause full reloads because shallow routing is not supported

D. The second push overrides shallow routing, causing a full reload

Solution

1. Step 1: Examine the two router.push calls

   The first call uses shallow routing, the second does not and triggers a full reload.

2. Step 2: Understand effect of second push on routing

   The second push overrides the first and causes a full page reload, negating shallow routing.

3. Final Answer:

   The second push overrides shallow routing, causing a full reload -> Option D

4. Quick Check:

   Non-shallow push cancels shallow routing [OK]

Hint: Later push without shallow cancels shallow routing [OK]

Common Mistakes:

• Assuming shallow routing applies to all pushes automatically
• Thinking shallow routing must be first push only
• Ignoring that non-shallow push triggers reload

5. You want to implement tab navigation in a Next.js page using shallow routing to update the URL query without losing component state. Which approach correctly achieves this?

hard

A. Use router.replace without shallow option to update URL and reset state

B. Use router.push with { shallow: true } when changing tabs and listen to router.query to update UI

C. Reload the page on every tab click to fetch fresh data

D. Manually manipulate window.location to change URL without Next.js router

Solution

1. Step 1: Identify shallow routing usage for tab navigation

   Using router.push with { shallow: true } updates URL query without full reload, preserving component state.

2. Step 2: Confirm UI updates from router.query changes

   Listening to router.query allows UI to react to tab changes smoothly without losing state.

3. Final Answer:

   Use router.push with { shallow: true } and listen to router.query -> Option B

4. Quick Check:

   Shallow routing + query listening = smooth tab navigation [OK]

Hint: Use router.push with shallow and watch router.query [OK]

Common Mistakes:

• Reloading page loses component state
• Using router.replace without shallow resets state
• Manipulating window.location breaks SPA behavior