Dynamic routes with parameters in Astro - Mini Project: Build & Apply

Dynamic Routes with Parameters in Astro

📖 Scenario: You are building a simple blog website using Astro. Each blog post has a unique ID, and you want to create pages that show the post details based on the post ID in the URL.

🎯 Goal: Create dynamic routes in Astro that use URL parameters to display blog post details.

📋 What You'll Learn

Create a data structure with blog posts and their details

Set up a configuration variable for the dynamic route parameter

Use Astro's dynamic route syntax to create a page that reads the post ID from the URL

Display the blog post title and content based on the URL parameter

💡 Why This Matters

🌍 Real World

Dynamic routes let websites show different content based on the URL, like user profiles or blog posts.

💼 Career

Understanding dynamic routes is essential for building modern web apps that respond to user input and URLs.

1

Create blog posts data

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

Astro

# Your code here

Hint

Use a JavaScript object with string keys for post IDs and objects for post details.

2

Set up dynamic route parameter

Create a constant called params and assign it the value of Astro.params to access the URL parameters.

Astro

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

// Your code here

Hint

Use Astro.params to get the dynamic route parameters inside your Astro component.

3

Get the post data using the route parameter

Create a constant called post and assign it the value of posts[params.id] to get the post details for the current URL parameter id.

Astro

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

const params = Astro.params;

// Your code here

Hint

Use bracket notation with params.id to get the correct post from the posts object.

4

Display the post title and content

Add HTML code to display the post title inside an <h1> tag and the post content inside a <p> tag using {post.title} and {post.content}.

Astro

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

const params = Astro.params;

const post = posts[params.id];

Hint

Use Astro's template syntax with curly braces to insert JavaScript values inside HTML.

Practice

1. What does a filename like [id].astro represent in Astro?

easy

A. A dynamic route that captures the id parameter from the URL

B. A static page named literally [id]

C. A component that cannot receive parameters

D. A special Astro configuration file

Solution

1. Step 1: Understand dynamic route syntax

   In Astro, square brackets in filenames like [id].astro define a dynamic route parameter named id.

2. Step 2: Recognize the purpose of the parameter

   This parameter captures part of the URL, allowing the page to change based on the URL segment.

3. Final Answer:

   A dynamic route that captures the id parameter from the URL -> Option A

4. Quick Check:

   Dynamic route = filename with [param] [OK]

Hint: Look for square brackets in filename for dynamic parameters [OK]

Common Mistakes:

• Thinking [id].astro is a static file
• Confusing parameter with component name
• Assuming parameters are optional by default

2. Which is the correct way to access a dynamic route parameter named slug inside an Astro component?

easy

A. Astro.query.slug

B. Astro.route.slug

C. Astro.params.slug

D. Astro.props.slug

Solution

1. Step 1: Recall Astro parameter access

   Astro provides dynamic route parameters inside the component via Astro.params.

2. Step 2: Use the parameter name as key

   To get the value of slug, use Astro.params.slug.

3. Final Answer:

   Astro.params.slug -> Option C

4. Quick Check:

   Access params with Astro.params.[name] [OK]

Hint: Use Astro.params to get dynamic route values [OK]

Common Mistakes:

• Using Astro.route or Astro.query instead of Astro.params
• Trying to access parameters via props
• Forgetting to use the exact parameter name

3. Given a file named src/pages/blog/[post].astro with this code snippet:

---
const postId = Astro.params.post;
---
Post ID: {postId}

What will be rendered when visiting /blog/42?

medium

A. Post ID: 42

B. Post ID: post

C. Post ID:

D. 404 Not Found

Solution

1. Step 1: Identify dynamic parameter value

   The URL /blog/42 matches the dynamic route [post].astro, so Astro.params.post is '42'.

2. Step 2: Render the parameter in the template

   The component outputs <h1>Post ID: {postId}</h1>, so it shows Post ID: 42.

3. Final Answer:

   <h1>Post ID: 42</h1> -> Option A

4. Quick Check:

   URL segment fills param = rendered value [OK]

Hint: URL segment replaces [param] and shows in Astro.params [OK]

Common Mistakes:

• Expecting literal 'post' instead of parameter value
• Assuming empty or missing parameter
• Confusing 404 with dynamic route handling

4. You have a dynamic route file named [user].astro but when visiting /john you get a runtime error: Cannot read property 'user' of undefined. What is the likely cause?

medium

A. Astro.params is only available in server components

B. You forgot to use Astro.params.user and accessed Astro.params directly

C. Dynamic routes cannot have parameters named 'user'

D. The filename should be {user}.astro instead of [user].astro

Solution

1. Step 1: Understand the error message

   The error says Cannot read property 'user' of undefined, meaning Astro.params is undefined or not accessed properly.

2. Step 2: Check parameter access syntax

   Accessing Astro.params.user is correct. If code tries to access Astro.params.user but Astro.params is undefined, it means Astro.params was not used or imported correctly.

3. Final Answer:

   You forgot to use Astro.params.user and accessed Astro.params directly -> Option B

4. Quick Check:

   Always use Astro.params.[param] to avoid undefined errors [OK]

Hint: Always access parameters via Astro.params.[name] [OK]

Common Mistakes:

• Using curly braces instead of square brackets in filename
• Assuming Astro.params is always defined globally
• Misnaming the parameter in code

5. You want to create a nested dynamic route in Astro to handle URLs like /products/electronics/123. Which file structure and parameter access is correct?

hard

A. Create src/pages/products/[category]/id.astro and access with Astro.params.id

B. Create src/pages/products/[category-id].astro and access with Astro.params['category-id']

C. Create src/pages/products/category/id.astro and access with Astro.params.category and Astro.params.id

D. Create src/pages/products/[category]/[id].astro and access with Astro.params.category and Astro.params.id

Solution

1. Step 1: Understand nested dynamic routes

   To match URLs like /products/electronics/123, you need nested folders with dynamic parameters: [category] and [id].

2. Step 2: Correct file structure and parameter access

   The correct structure is src/pages/products/[category]/[id].astro. Inside, access parameters as Astro.params.category and Astro.params.id.

3. Final Answer:

   Create src/pages/products/[category]/[id].astro and access with Astro.params.category and Astro.params.id -> Option D

4. Quick Check:

   Nested folders with [param] = nested params [OK]

Hint: Use nested folders with [param] for multi-level dynamic routes [OK]

Common Mistakes:

• Combining multiple params in one filename incorrectly
• Using static folder names instead of dynamic
• Accessing parameters that don't exist in the route