Shallow routing concept in NextJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when shallow routing is used in Next.js?

Consider a Next.js page that uses shallow routing to change the URL query without running getServerSideProps again. What is the expected behavior?

NextJS

import { useRouter } from 'next/router';

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

  function changeQuery() {
    router.push({ pathname: '/page', query: { tab: '2' } }, undefined, { shallow: true });
  }

  return (
    <>
      <p>Current tab: {router.query.tab || '1'}</p>
      <button onClick={changeQuery}>Change Tab</button>
    </>
  );
}

A The URL does not update, but the component re-renders with new query values.

B The URL updates but the component does not re-render.

C The URL updates and the page fully reloads, calling getServerSideProps again.

D The URL updates and the component re-renders without calling getServerSideProps or getStaticProps again.

💡 Hint

Shallow routing updates the URL without a full page reload or data fetching methods running again.

Shallow routing in Next.js changes the URL and updates the router state without running data fetching methods like getServerSideProps again. This allows the component to re-render with new query parameters efficiently.

📝 Syntax

intermediate

Which code snippet correctly uses shallow routing in Next.js?

Select the code snippet that correctly performs shallow routing to update the URL query without a full page reload.

A router.push('/page?tab=2', undefined, { shallow: true });

B router.replace('/page?tab=2', undefined, { shallow: false });

C router.push('/page?tab=2', undefined, { shallow: false });

D router.replace('/page?tab=2', undefined, { shallow: true });

💡 Hint

Shallow routing requires the shallow option set to true and usually uses router.push to add a new history entry.

Using router.push with the third argument { shallow: true } correctly enables shallow routing. router.replace can also be used but is less common for shallow routing that adds history entries.

🔧 Debug

advanced

Why does shallow routing not update the component state as expected?

A developer uses shallow routing to update the URL query, but the component does not reflect the new query value. What is the most likely cause?

NextJS

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

export default function Page() {
  const router = useRouter();
  const [tab, setTab] = useState(router.query.tab || '1');

  useEffect(() => {
    setTab(router.query.tab || '1');
  }, []);

  function changeTab() {
    router.push({ pathname: '/page', query: { tab: '2' } }, undefined, { shallow: true });
  }

  return (
    <>
      <p>Current tab: {tab}</p>
      <button onClick={changeTab}>Change Tab</button>
    </>
  );
}

A Shallow routing does not update the URL query, so tab remains the same.

B The useEffect has an empty dependency array, so it does not update tab when router.query changes.

C The router.push call is missing the shallow option, causing a full reload.

D The initial state uses router.query.tab which is undefined, causing an error.

💡 Hint

Check how useEffect dependencies affect state updates when router.query changes.

The useEffect hook runs only once because of the empty dependency array. It does not respond to changes in router.query, so the tab state does not update when shallow routing changes the URL.

🧠 Conceptual

advanced

What is a key limitation of shallow routing in Next.js?

Which of the following is a limitation when using shallow routing in Next.js?

A It does not trigger getServerSideProps or getStaticProps, so data fetching is not re-run automatically.

B It causes a full page reload, losing client-side state.

C It cannot update the URL query parameters.

D It disables client-side navigation and forces server navigation.

💡 Hint

Think about what shallow routing skips compared to normal routing.

Shallow routing updates the URL and component state but does not trigger Next.js data fetching methods like getServerSideProps or getStaticProps again. This means data may not refresh automatically.

❓ state_output

expert

What is the value of router.query.tab after shallow routing?

Given the following code, what will be logged to the console after clicking the button?

NextJS

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

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

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

  function changeTab() {
    router.push({ pathname: '/page', query: { tab: '3' } }, undefined, { shallow: true });
  }

  return <button onClick={changeTab}>Change Tab</button>;
}

A '2'

B undefined

C '3'

D null

💡 Hint

Shallow routing updates the URL query and router.query state immediately.

When shallow routing updates the URL query, router.query reflects the new query parameters immediately, triggering the useEffect and logging '3'.

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