Dynamic routes with parameters in Astro

Introduction

Dynamic routes let your website show different pages based on the URL. This means you can create one page that changes depending on what the user clicks or types.

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

Displaying blog posts where each post has its own URL based on the title or ID.

Creating product pages in an online store where each product has a unique page.

Building event pages where each event has a date or name in the URL.

Syntax

Astro

src/pages/[param].astro

---
const { params } = Astro;
const value = params.param;
---

<h1>Value is: {value}</h1>

Use square brackets [param] in the filename to mark a dynamic part of the URL.

Access the parameter inside the component with Astro.params.param.

Examples

This page shows a welcome message for any username in the URL like /john or /alice.

Astro

src/pages/[username].astro

---
const { params } = Astro;
const username = params.username;
---

<h1>Welcome, {username}!</h1>

This page displays a blog post based on the slug in the URL, for example /blog/my-first-post.

Astro

src/pages/blog/[slug].astro

---
const { params } = Astro;
const slug = params.slug;
---

<h1>Blog post: {slug}</h1>

Sample Program

This component creates a product page that changes based on the product ID in the URL. For example, visiting /product/123 will show "You are viewing product with ID: 123".

Astro

src/pages/product/[id].astro

---
const { params } = Astro;
const productId = params.id;
---

<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Product {productId}</title>
  </head>
  <body>
    <main>
      <h1>Product Page</h1>
      <p>You are viewing product with ID: {productId}</p>
    </main>
  </body>
</html>

Important Notes

Dynamic route files must be inside the src/pages folder.

Parameter names in brackets should be simple and descriptive.

You can have multiple parameters like [category]/[id].astro for nested dynamic routes.

Summary

Dynamic routes let you create flexible pages that change based on the URL.

Use square brackets in filenames to define parameters.

Access parameters inside your component with Astro.params.

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