Dynamic routes with [param] in NextJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a dynamic route in Next.js?

A dynamic route in Next.js is a page route that uses square brackets [param] in the filename to capture variable parts of the URL, allowing the page to render different content based on the URL segment.

beginner

How do you define a dynamic route for a user profile page with a user ID in Next.js?

You create a file named [userId].js inside the pages or app directory. The [userId] part captures the user ID from the URL, like /profile/123, where 123 is the userId.

intermediate

How do you access the dynamic parameter inside a Next.js page component?

You use the useRouter hook from 'next/router' or the params object in server components to get the dynamic parameter value from the URL.

beginner

What is the difference between a static route and a dynamic route in Next.js?

A static route has a fixed path like /about, while a dynamic route uses [param] to match many paths like /product/1, /product/2, where the param changes.

intermediate

Can you have multiple dynamic segments in a Next.js route? How?

Yes, you can have multiple dynamic segments by naming files like [category]/[id].js. This captures two parameters from the URL, for example /books/123.

What does the file name [postId].js represent in Next.js routing?

A A dynamic route capturing postId from the URL

B A static route named postId

C A component that cannot be routed

D A special API route

Files with [param] in their name define dynamic routes that capture the param value from the URL.

How do you get the value of a dynamic route parameter inside a client component?

A Using window.location.pathname

B Using getStaticProps only

C Using useRouter hook from 'next/router'

D Using CSS selectors

The useRouter hook provides access to the dynamic route parameters in client components.

Which URL matches the dynamic route file [category]/[id].js?

A /category

B /books/123

C /123/books

D /books

The URL /books/123 matches the dynamic segments category=books and id=123.

What happens if you visit a dynamic route URL that does not match any file?

A Next.js shows a 404 page

B Next.js redirects to home

C Next.js crashes

D Next.js shows a blank page

If no matching route file exists, Next.js shows the 404 not found page.

Can dynamic routes be nested inside folders in Next.js?

A Only static routes can be nested

B No, all dynamic routes must be in root

C Dynamic routes must be flat files

D Yes, you can nest dynamic routes in folders

Dynamic routes can be nested inside folders to create complex URL structures.

Explain how to create and use a dynamic route with [param] in Next.js.

Think about how the file name relates to the URL and how to get the value inside the component.

Describe the difference between static and dynamic routes in Next.js and when to use each.

Consider how URLs look and what content changes.

Practice

1. What does the file name [id].js inside the pages folder in Next.js represent?

easy

A. A static page named literally 'id'

B. A dynamic route where id is a variable part of the URL

C. A special API route for handling requests

D. A CSS module file for styling

Solution

1. Step 1: Understand Next.js dynamic route naming

   Files with names in square brackets like [id].js represent dynamic routes where the part inside brackets is a variable.

2. Step 2: Interpret the meaning of [id].js

   This means the URL can have any value in place of id, and the page will render accordingly.

3. Final Answer:

   A dynamic route where id is a variable part of the URL -> Option B

4. Quick Check:

   Dynamic route = [param] file name [OK]

Hint: Square brackets mean dynamic URL part [OK]

Common Mistakes:

• Thinking it's a static page named 'id'
• Confusing with API routes
• Assuming it's a styling file

2. Which of the following is the correct way to access the dynamic parameter slug in a Next.js page component inside pages/[slug].js?

easy

A. const { slug } = props.params;

B. const slug = params.slug;

C. const slug = useRouter().query.slug;

D. const slug = window.location.slug;

Solution

1. Step 1: Recall how to get dynamic params in Next.js client-side

   Next.js provides the useRouter hook to access route parameters via router.query.

2. Step 2: Identify correct syntax

   The correct way is const slug = useRouter().query.slug; to get the dynamic slug value.

3. Final Answer:

   const slug = useRouter().query.slug; -> Option C

4. Quick Check:

   useRouter().query.param gets dynamic route param [OK]

Hint: Use useRouter().query.param for dynamic params [OK]

Common Mistakes:

• Trying to destructure from props.params directly
• Using window.location which doesn't have slug
• Using undefined variable params

3. Given the file pages/blog/[postId].js with this code:

import { useRouter } from 'next/router';
export default function Post() {
  const router = useRouter();
  return <div>Post ID: {router.query.postId}</div>;
}

What will be rendered when the user visits /blog/42?

medium

A. Post ID: postId

B. Error: router is undefined

C. Post ID: undefined

D. Post ID: 42

Solution

1. Step 1: Understand dynamic route matching

   The file [postId].js matches URLs like /blog/42 and sets postId to '42'.

2. Step 2: Check how router.query.postId is used

   The component uses router.query.postId to display the dynamic value, so it will show '42'.

3. Final Answer:

   Post ID: 42 -> Option D

4. Quick Check:

   Dynamic param value shown = 42 [OK]

Hint: router.query.param shows URL dynamic value [OK]

Common Mistakes:

• Expecting literal 'postId' string output
• Assuming undefined because of initial render
• Thinking router is not defined

4. You have a dynamic route file pages/product/[productId].js. The component tries to access params.productId directly but gets an error. What is the likely cause?

medium

A. The component should use useRouter().query.productId instead of params.productId

B. The file name should be productId.js without brackets

C. Dynamic routes do not support parameters

D. You must import params from 'next/params'

Solution

1. Step 1: Identify how to access dynamic params in client components

   In Next.js, dynamic route params are accessed via useRouter().query in client components, not directly from params.

2. Step 2: Understand why params.productId causes error

   Using params.productId without proper context or props causes undefined errors.

3. Final Answer:

   The component should use useRouter().query.productId instead of params.productId -> Option A

4. Quick Check:

   Use useRouter().query for dynamic params [OK]

Hint: Use useRouter().query, not params directly [OK]

Common Mistakes:

• Trying to access params without props or hooks
• Renaming file incorrectly
• Expecting automatic import of params

5. You want to create a dynamic route in Next.js that matches URLs like /user/123/profile. Which folder and file structure inside app directory correctly implements this using dynamic segments?

hard

A. app/user/[id]/profile/page.js

B. app/user/profile/[id].js

C. app/user/[id]-profile/page.js

D. app/user/[id]/profile.js

Solution

1. Step 1: Understand Next.js app router folder structure

   Each folder represents a URL segment. Dynamic segments use square brackets like [id].

2. Step 2: Map URL /user/123/profile to folders

   The URL has three parts: 'user', dynamic '123', and 'profile'. So folders should be user/[id]/profile with a page.js inside.

3. Final Answer:

   app/user/[id]/profile/page.js -> Option A

4. Quick Check:

   Dynamic folder inside URL path = [param] folder [OK]

Hint: Dynamic segments are folders with [param] in app router [OK]

Common Mistakes:

• Placing dynamic param after static folder incorrectly
• Using dash instead of folder for dynamic segment
• Putting dynamic param in wrong folder level