Dynamic route parameters in Svelte - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the rendered output for this dynamic route?

Given a SvelteKit route file named src/routes/blog/[slug].svelte with the following code, what will be displayed when navigating to /blog/hello-world?

Svelte

<script>
  export let params;
</script>

<h1>Blog Post: {params.slug}</h1>

A <h1>Blog Post: </h1>

B <h1>Blog Post: [slug]</h1>

C <h1>Blog Post: params.slug</h1>

D <h1>Blog Post: hello-world</h1>

💡 Hint

Dynamic route parameters are passed as params to the component.

The [slug] in the filename captures the URL part after /blog/ and passes it as params.slug. So navigating to /blog/hello-world sets params.slug to hello-world.

📝 Syntax

intermediate

Which code correctly accesses a dynamic parameter in a SvelteKit page?

Choose the option that correctly accesses the dynamic route parameter id in a file named src/routes/user/[id].svelte.

A <script>let userId = $page.params.id;</script>

B <script>export let params; let userId = params.id;</script>

C <script>import { page } from '$app/stores'; let userId = page.params.id;</script>

D <script>export let id; let userId = id;</script>

💡 Hint

Dynamic parameters are passed as params props to the page component.

In SvelteKit, dynamic route parameters are passed as params to the page component as props. So you must declare export let params; and then access params.id.

❓ state_output

advanced

What is the value of currentId after navigation?

Consider this SvelteKit component in src/routes/product/[id].svelte:

<script>
  export let params;
  let currentId = params.id;
</script>

<h2>Product ID: {currentId}</h2>

If the user navigates from /product/123 to /product/456 without a full page reload, what will be the value of currentId?

A 123

B 456

C undefined

D An error is thrown

💡 Hint

Think about how export let params works with client-side navigation.

The params prop is set only when the component is created. Navigating client-side does not recreate the component, so currentId remains the initial value 123. To update on navigation, you must react to params changes.

🔧 Debug

advanced

Why does this dynamic route component show an empty slug?

Given this SvelteKit component src/routes/[slug].svelte:

<script>
  export let params;
</script>

<p>Slug: {params.slug}</p>

When navigating to /hello, the page shows Slug: (empty). What is the most likely cause?

A The <code>params</code> prop is missing the <code>export let</code> declaration, so it is undefined

B The <code>params</code> prop is not passed automatically; you must import it from <code>$page</code> store

C The route parameter name in the filename does not match the accessed property; it should be <code>params.hello</code>

D The route file is named incorrectly; it should be <code>[slug].js</code> instead of <code>[slug].svelte</code>

💡 Hint

Check how props are declared in Svelte components.

In SvelteKit, dynamic route parameters are passed as props named params. To access them, you must declare export let params;. Without this, params is undefined, so params.slug is empty.

🧠 Conceptual

expert

How does SvelteKit handle multiple dynamic parameters in nested routes?

Consider these two route files in SvelteKit:

• src/routes/shop/[category]/[item].svelte
• src/routes/shop/[category]/index.svelte

If a user navigates to /shop/electronics/phone, which parameters are available in [item].svelte and what are their values?

A Only <code>params.item</code> is available with value <code>phone</code>; <code>params.category</code> is undefined

B Only <code>params.category</code> is available with value <code>electronics</code>; <code>params.item</code> is undefined

C Both <code>params.category</code> and <code>params.item</code> are available with values <code>electronics</code> and <code>phone</code> respectively

D No <code>params</code> are available because nested dynamic routes do not pass parameters

💡 Hint

Think about how nested dynamic segments combine their parameters.

SvelteKit merges all dynamic parameters from the full route path. So in /shop/electronics/phone, params.category is electronics and params.item is phone in the [item].svelte component.

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