Dynamic route segments in NextJS - Mini Project: Build & Apply

Dynamic Route Segments in Next.js

📖 Scenario: You are building a blog website using Next.js. Each blog post has a unique ID, and you want to create pages that show the content of each post dynamically based on the URL.

🎯 Goal: Create a dynamic route segment in Next.js to display blog post details based on the post ID from the URL.

📋 What You'll Learn

Create a data structure with blog posts and their details

Add a configuration variable for the default post ID

Use Next.js dynamic route segment to fetch the post ID from the URL

Display the blog post title and content dynamically on the page

💡 Why This Matters

🌍 Real World

Dynamic route segments let websites show different content pages based on URL parts, like user profiles or blog posts.

💼 Career

Understanding dynamic routes is essential for building modern web apps with Next.js, a popular React framework used in many companies.

1

Create blog posts data

Create a constant called posts that is an object with these exact entries: "1": { title: "First Post", content: "This is the first post." }, "2": { title: "Second Post", content: "This is the second post." }, and "3": { title: "Third Post", content: "This is the third post." }.

NextJS

# Your code here

Hint

Use a constant object named posts with keys as strings "1", "2", and "3".

2

Add default post ID configuration

Create a constant called defaultPostId and set it to the string "1".

NextJS

const posts = {
  "1": { title: "First Post", content: "This is the first post." },
  "2": { title: "Second Post", content: "This is the second post." },
  "3": { title: "Third Post", content: "This is the third post." }
};

# Your code here

Hint

Define a constant defaultPostId with the value "1" as a string.

3

Create dynamic route component

Create a default exported React functional component called PostPage that uses the Next.js useRouter hook to get the postId from router.query. Use defaultPostId if postId is undefined. Then get the post data from posts[postId].

NextJS

const posts = {
  "1": { title: "First Post", content: "This is the first post." },
  "2": { title: "Second Post", content: "This is the second post." },
  "3": { title: "Third Post", content: "This is the third post." }
};

const defaultPostId = "1";

// Your code here

Hint

Use useRouter to get postId from router.query. Use ?? to fallback to defaultPostId.

4

Add dynamic route file and export

Create a file named [postId].jsx inside the app directory and place the PostPage component code inside it. Ensure the file exports the PostPage component as default.

NextJS

import { useRouter } from 'next/router';

const posts = {
  "1": { title: "First Post", content: "This is the first post." },
  "2": { title: "Second Post", content: "This is the second post." },
  "3": { title: "Third Post", content: "This is the third post." }
};

const defaultPostId = "1";

export default function PostPage() {
  const router = useRouter();
  const postId = router.query.postId ?? defaultPostId;
  const post = posts[postId];

  return (
    
      {post?.title}
      {post?.content}
    
  );
}

# Your code here

Hint

Save this component in a file named [postId].jsx inside the app folder to enable dynamic routing.

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