Dynamic route segments in NextJS

Introduction

Dynamic route segments let you create pages that change based on the URL. This helps show different content without making many separate pages.

Showing user profiles where each user has a unique ID in the URL.

Displaying blog posts where the post ID or slug changes per article.

Creating product pages where each product has its own page based on its ID.

Building category pages where the category name is part of the URL.

Handling any page where part of the URL needs to be flexible and dynamic.

Syntax

NextJS

app/[segment]/page.js

Use square brackets [] around the folder or file name to mark it as dynamic.

The name inside brackets becomes a variable you can use in your code.

Examples

This creates a dynamic route where userId changes based on the URL, like /123 or /alice.

NextJS

app/[userId]/page.js

This sets up dynamic blog post pages where slug is the post identifier in the URL.

NextJS

app/blog/[slug]/page.js

Each product page URL uses a dynamic productId segment.

NextJS

app/products/[productId]/page.js

Sample Program

This component shows a user profile page. It reads the dynamic userId from the URL and displays it on the page.

For example, visiting /123 will show "User ID: 123".

NextJS

'use client';

import { useParams } from 'next/navigation';

export default function UserPage() {
  const params = useParams();
  return (
    <main>
      <h1>User Profile</h1>
      <p>User ID: {params.userId}</p>
    </main>
  );
}

// File path: app/[userId]/page.js

Important Notes

Dynamic segments must be inside the app folder in Next.js 13+ App Router.

You can access the dynamic segment value using the useParams() hook.

Dynamic routes help keep your app organized and avoid creating many similar files.

Summary

Dynamic route segments let URLs change parts to show different content.

Use square brackets [] in folder or file names to create dynamic routes.

Access the dynamic part in your component with useParams().

Practice

1. In Next.js, what does a file named [id].js inside the pages folder represent?

easy

A. A configuration file for setting environment variables

B. A static page that only matches the URL /id

C. A special API route for handling requests with an id parameter

D. A dynamic route segment that matches any value in the URL at that position

Solution

1. Step 1: Understand Next.js routing conventions

   Files inside the pages folder define routes. Square brackets [] indicate dynamic segments.

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

   The file [id].js matches any URL segment in that position and passes it as a parameter named id.

3. Final Answer:

   A dynamic route segment that matches any value in the URL at that position -> Option D

4. Quick Check:

   Dynamic route = [segment] [OK]

Hint: Square brackets mean dynamic URL part in Next.js routes [OK]

Common Mistakes:

• Thinking [id].js is a static page
• Confusing dynamic routes with API routes
• Assuming it matches only the literal 'id'

2. Which of the following is the correct syntax to define a dynamic route segment for a Next.js page that captures a username?

easy

A. pages/:username.js

B. pages/username.js

C. pages/[username].js

D. pages/{username}.js

Solution

1. Step 1: Recall Next.js dynamic route syntax

   Dynamic segments use square brackets around the parameter name inside the pages folder.

2. Step 2: Match syntax for username parameter

   The correct syntax is [username].js to capture the username dynamically.

3. Final Answer:

   pages/[username].js -> Option C

4. Quick Check:

   Dynamic segment uses [param] syntax [OK]

Hint: Use square brackets for dynamic route names [OK]

Common Mistakes:

• Using colon or curly braces instead of square brackets
• Naming the file without brackets for dynamic routes
• Confusing dynamic routes with static filenames

3. Given the file structure:
pages/blog/[slug].js
and the URL /blog/hello-world, what will be the value of the slug parameter inside the page component?

medium

A. "hello-world"

B. "blog"

C. "[slug]"

D. undefined

Solution

1. Step 1: Identify dynamic segment from file name

   The file [slug].js captures the URL segment after /blog/ as slug.

2. Step 2: Match URL segment to parameter

   For URL /blog/hello-world, the segment hello-world is assigned to slug.

3. Final Answer:

   "hello-world" -> Option A

4. Quick Check:

   URL segment after folder = slug value [OK]

Hint: Dynamic segment captures URL part matching filename [OK]

Common Mistakes:

• Using folder name as parameter value
• Assuming parameter is the literal filename
• Expecting undefined if parameter not explicitly passed

4. Consider this Next.js dynamic route file: pages/product/[id].js. Which of the following code snippets correctly accesses the id parameter inside the component?

medium

A. const router = useRouter(); const { id } = router.query;

B. const { id } = props.params;

C. const id = useParams().id;

D. const id = getIdFromUrl();

Solution

1. Step 1: Recall how to access route params in Next.js pages

   Next.js uses the useRouter hook from next/router to access query parameters.

2. Step 2: Identify correct syntax for extracting id

   The correct way is const router = useRouter(); const { id } = router.query;.

3. Final Answer:

   const router = useRouter(); const { id } = router.query; -> Option A

4. Quick Check:

   useRouter().query gives dynamic params [OK]

Hint: Use useRouter().query to get dynamic route params [OK]

Common Mistakes:

• Using props.params which is not standard in Next.js pages
• Using useParams() which is from React Router, not Next.js
• Calling undefined functions like getIdFromUrl()

5. You want to create a nested dynamic route in Next.js to handle URLs like /dashboard/user/123 where 123 is a user ID. Which file structure correctly implements this?

hard

A. pages/dashboard/[user]/[id].js

B. pages/dashboard/user/[id].js

C. pages/dashboard/[id].js

D. pages/[dashboard]/user/[id].js

Solution

1. Step 1: Analyze the URL structure

   The URL /dashboard/user/123 has three segments: dashboard, user, and a dynamic id.

2. Step 2: Match file structure to URL segments

   Static segments dashboard and user are folders, and [id].js captures the dynamic user ID.

3. Step 3: Verify options

   pages/dashboard/user/[id].js matches the folder structure exactly. Options B and D incorrectly treat static parts as dynamic. pages/dashboard/[id].js misses the user folder.

4. Final Answer:

   pages/dashboard/user/[id].js -> Option B

5. Quick Check:

   Static folders + [id].js for dynamic segment [OK]

Hint: Match URL parts to folders; dynamic parts use [param].js [OK]

Common Mistakes:

• Making static parts dynamic segments
• Omitting intermediate folders for static URL parts
• Confusing order of folders and dynamic files