Why Dynamic route segments in NextJS? - Purpose & Use Cases

The Big Idea

Discover how one file can replace hundreds of pages and save you hours of work!

The Scenario

Imagine building a website where each user has a unique profile page, and you have to create a separate file or page for every single user manually.

The Problem

Manually creating pages for each user is impossible to maintain, slow to update, and leads to a huge mess as the number of users grows.

The Solution

Dynamic route segments let you create one flexible page that automatically adapts to different URLs, showing the right content without extra files.

Before vs After

✗ Before

pages/user-john.js
pages/user-mary.js

✓ After

pages/user/[username].js

What It Enables

It enables building scalable websites that respond to many different URLs with just a few smart files.

Real Life Example

Think of an online store where each product has its own page generated dynamically from the product ID in the URL.

Key Takeaways

Manual page creation for each URL is slow and unmanageable.

Dynamic route segments create flexible pages that handle many URLs.

This makes websites easier to build and scale.

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