Dynamic route parameters in Svelte

Introduction

Dynamic route parameters let your app show different pages based on parts of the URL. This helps create pages that change depending on what the user clicks or types.

Showing a user profile page based on the user ID in the URL.

Displaying a blog post page using the post's unique slug from the URL.

Creating product pages where each product has its own URL with its ID.

Building a details page for items where the item ID is part of the URL.

Syntax

Svelte

/src/routes/[parameter]/+page.svelte

The square brackets [] around a name in the filename tell SvelteKit this part is dynamic.

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

Examples

This file handles URLs like /123 or /abc. The id is dynamic and changes based on the URL.

Svelte

/src/routes/[id]/+page.svelte

Inside the component, you get the dynamic part from params. Here, params.id shows the value from the URL.

Svelte

<script>
  export let params;
</script>

<h1>User ID: {params.id}</h1>

This route uses slug as the dynamic parameter, useful for blog post URLs like /blog/my-first-post.

Svelte

/src/routes/blog/[slug]/+page.svelte

Sample Program

This SvelteKit component shows a product page. The URL should look like /product/123, where 123 is the product ID. The component reads this ID from params.productId and displays it.

Svelte

<script>
  export let params;
</script>

<h1>Product Page</h1>
<p>Product ID: {params.productId}</p>

Important Notes

You must export params to access dynamic route values.

Dynamic routes can be nested, like /blog/[slug]/comments/+page.svelte.

Use descriptive parameter names to keep your code clear.

Summary

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

Use square brackets in filenames to define dynamic parts.

Access the dynamic value inside your component via the params object.

Practice

1. What does a filename like [id].svelte represent in a SvelteKit project?

easy

A. A dynamic route where id is a variable part of the URL

B. A static page named literally 'id'

C. A component that cannot be accessed via URL

D. A special file for global styles

Solution

1. Step 1: Understand filename brackets in SvelteKit

   Square brackets in filenames define dynamic segments in routes, meaning the part inside brackets is a variable.

2. Step 2: Interpret [id].svelte

   This means the page matches URLs like /123 or /abc, where id changes dynamically.

3. Final Answer:

   A dynamic route where id is a variable part of the URL -> Option A

4. Quick Check:

   Filename with brackets = dynamic route [OK]

Hint: Brackets in filename mean dynamic URL part [OK]

Common Mistakes:

• Thinking bracket means static filename
• Confusing dynamic route with component name
• Assuming it is for styles or scripts

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

easy

A. Using export let params; in the script

B. Using window.slug in the script

C. Using const { slug } = params; inside load function

D. Using this.slug in the component

Solution

1. Step 1: Recall how SvelteKit passes route params

   Dynamic route parameters are passed to the page component as a params prop object.

2. Step 2: Declare the prop in the script

   Inside the page component (+page.svelte) script, use export let params; to receive it, then access params.slug.

3. Final Answer:

   Using export let params; in the script -> Option A

4. Quick Check:

   export let params; receives route params [OK]

Hint: export let params; in page script [OK]

Common Mistakes:

• Using export let slug; (wrong prop name)
• Accessing params from window or this
• Confusing with load function params

3. Given a file named src/routes/blog/[postId].svelte with this code:

  <script>
    export let params;
  </script>

  <h1>Post ID: {params.postId}</h1>

What will be rendered when visiting /blog/42?

medium

A. Post ID: postId

B. Post ID: 42

C. Post ID: {params.postId}

D. Error: params is undefined

Solution

1. Step 1: Understand dynamic route parameter passing

   The [postId].svelte file captures the URL segment after /blog/ as postId and passes it as params.postId.

2. Step 2: Check how params is used in the component

   The component uses {params.postId} inside the heading, so it will display the actual value from the URL.

3. Final Answer:

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

4. Quick Check:

   Dynamic param value shown = 42 [OK]

Hint: Dynamic param in URL shows inside {params.paramName} [OK]

Common Mistakes:

• Expecting literal string 'postId' instead of value
• Forgetting to export params
• Using params without export or load

4. You have a dynamic route file [user].svelte but when you visit /john, you get an error: params is undefined. What is the likely cause?

medium

A. You must use window.params to access parameters

B. You named the file incorrectly; it should be {user}.svelte

C. You forgot to export let params in the script

D. Dynamic routes do not support parameters

Solution

1. Step 1: Check how params are accessed in SvelteKit

   Dynamic route parameters are passed as a prop named params which must be exported in the script.

2. Step 2: Identify missing export

   If let params is not exported, the component cannot access it, causing params is undefined.

3. Final Answer:

   You forgot to export let params in the script -> Option C

4. Quick Check:

   Export params to access dynamic route data [OK]

Hint: Always export let params to use route parameters [OK]

Common Mistakes:

• Using curly braces in filename instead of brackets
• Trying to access params from window object
• Assuming dynamic routes don't pass params

5. You want to create a nested dynamic route in SvelteKit to show a user's post detail at URL /user/123/post/456. Which file structure and parameter access is correct?

hard

A. Files: src/routes/user/[userId]/post.svelteAccess: params.userId only

B. Files: src/routes/user/[userId]/post/[postId].svelteAccess: params.user and params.post

C. Files: src/routes/user/post/[postId].svelteAccess: params.userId and params.postId

D. Files: src/routes/user/[userId]/post/[postId].svelteAccess: params.userId and params.postId

Solution

1. Step 1: Understand nested dynamic routes in SvelteKit

   To match URL segments like /user/123/post/456, you create nested folders with dynamic filenames for each variable part.

2. Step 2: Confirm file structure and parameter names

   The correct structure is user/[userId]/post/[postId].svelte, and inside the component, you access params.userId and params.postId.

3. Final Answer:

   Files: src/routes/user/[userId]/post/[postId].svelte and access params.userId and params.postId -> Option D

4. Quick Check:

   Nested dynamic folders match URL segments [OK]

Hint: Use nested folders with brackets for each dynamic segment [OK]

Common Mistakes:

• Using wrong param names inside params object
• Missing nested folder for second dynamic segment
• Trying to access params not defined by filename