Error pages (+error.svelte) - Mini Project: Build & Apply

Create a Custom Error Page with +error.svelte in SvelteKit

📖 Scenario: You are building a website using SvelteKit. You want to show a friendly error page whenever something goes wrong, like a missing page or a server error.

🎯 Goal: Create a custom error page using the +error.svelte file that shows the error status and message clearly to the user.

📋 What You'll Learn

Create a +error.svelte file with a script block that receives error and status props

Display the error status and message in the page content

Add a friendly heading and a short explanation

Use semantic HTML and accessible roles

Style the error page with simple CSS for clarity and responsiveness

💡 Why This Matters

🌍 Real World

Custom error pages improve user experience by showing friendly messages when something goes wrong on a website.

💼 Career

Knowing how to create error pages is important for frontend developers working with SvelteKit or similar frameworks to handle errors gracefully.

1

Create the basic +error.svelte file with props

Create a +error.svelte file. Inside it, write a <script> block that declares export let error and export let status to receive error details.

Svelte

  // Declare props error and status
  // Your code here

Hint

Use export let to declare props in Svelte components.

2

Add HTML structure to display error status and message

Below the <script> block, add a <main> element with a heading <h1> that shows Error {status}. Then add a paragraph <p> that displays {error.message}.

Svelte

  export let error;
  export let status;



  
  

Hint

Use curly braces {} to insert variables in Svelte templates.

3

Add a friendly explanation and semantic roles

Inside the <main>, add a second paragraph <p> with the text Sorry, something went wrong. Also add role="alert" to the <main> element for accessibility.

Svelte

  export let error;
  export let status;



  Error {status}
  {error.message}
  
  

Hint

Use role="alert" on the main container to notify screen readers of important messages.

4

Add simple CSS styles for clarity and responsiveness

Add a <style> block below the HTML. Inside it, style main with max-width: 30rem;, margin: 2rem auto;, padding: 1rem;, border: 1px solid #ccc;, and border-radius: 0.5rem;. Also style h1 with color: #c00; and font-size: 2rem;.

Svelte

  export let error;
  export let status;



  Error {status}
  {error.message}
  Sorry, something went wrong.



  /* Add styles for main and h1 here */
  /* Your code here */

Hint

Use CSS properties inside a <style> block to style your error page.

Practice

1. What is the main purpose of the +error.svelte file in a SvelteKit project?

easy

A. To handle user authentication

B. To display a custom error page when an error occurs in the app

C. To define global styles for the app

D. To manage routing between pages

Solution

1. Step 1: Understand the role of +error.svelte

   This file is specifically designed to show error messages when something goes wrong in the app.

2. Step 2: Compare with other options

   Authentication, styling, and routing are handled elsewhere, not in +error.svelte.

3. Final Answer:

   To display a custom error page when an error occurs in the app -> Option B

4. Quick Check:

   Error page = +error.svelte [OK]

Hint: Remember: +error.svelte shows errors, not routes or styles [OK]

Common Mistakes:

• Confusing error page with routing or styling files
• Thinking +error.svelte handles authentication
• Assuming it is for normal page content

2. Which of the following is the correct way to access the HTTP status code inside +error.svelte?

easy

A. {error.status}

B. {params.status}

C. {error.message}

D. {status}

Solution

1. Step 1: Recall SvelteKit error props

   In +error.svelte, the status is passed as a separate prop, not inside error.

2. Step 2: Check each option

   {error.status} is incorrect because error holds the error object, but status is separate. {status} is correct. {error.message} is for the message, not status. {params.status} is unrelated.

3. Final Answer:

   {status} -> Option D

4. Quick Check:

   Status code = {status} [OK]

Hint: Status is a separate prop, not inside error object [OK]

Common Mistakes:

• Using {error.status} instead of {status}
• Confusing error message with status code
• Trying to access status from params

3. Given this +error.svelte snippet:

<script>
  export let error;
  export let status;
</script>

<h1>Error {status}</h1>
<p>{error.message}</p>

What will be displayed if status is 404 and error.message is "Page not found"?

medium

A. Error 404Page not found

B. Error Page not found404

C. Error 0undefined

D. Error 404undefined

Solution

1. Step 1: Substitute values in template

   The {status} is 404, so <h1> shows "Error 404". The {error.message} is "Page not found", so <p> shows that text.

2. Step 2: Confirm output matches option

   Error 404
   Page not found matches exactly: "Error 404" and "Page not found". Others have wrong order or undefined values.

3. Final Answer:

   Error 404
   Page not found -> Option A

4. Quick Check:

   Display status and message correctly [OK]

Hint: Match variable names exactly to output text [OK]

Common Mistakes:

• Mixing status and message order
• Assuming undefined values
• Confusing error.message with status

4. You wrote this +error.svelte code:

<script>
  export let error;
</script>

<h1>Error {status}</h1>
<p>{error.message}</p>

But when an error occurs, the page shows Error undefined. What is the problem?

medium

A. You need to import status from another file

B. You should use {error.status} instead of {status}

C. You forgot to export the status prop

D. The error object does not have a message property

Solution

1. Step 1: Identify missing prop export

   The code uses {status} but does not export status from the script, so it is undefined.

2. Step 2: Check other options

   {error.status} is incorrect because status is a separate prop. Importing status is not needed. error.message exists, so that is not the issue.

3. Final Answer:

   You forgot to export the status prop -> Option C

4. Quick Check:

   Export all props used in template [OK]

Hint: Always export props you use in template [OK]

Common Mistakes:

• Using {status} without exporting it
• Trying to access status inside error object
• Assuming error.message is missing

5. You want to create a custom error page that shows a special message for 404 errors and a generic message for others. Which +error.svelte code correctly implements this?

hard

A. <script>
export let error;
export let status;
</script>

<h1>Error {status}</h1>
<p>{status === 404 ? 'Page not found' : error.message}</p>

B. <script>
export let error;
</script>

<h1>Error {error.status}</h1>
<p>{error.message === 404 ? 'Page not found' : error.message}</p>

C. <script>
export let error;
export let status;
</script>

<h1>Error {status}</h1>
<p>{error.message === 404 ? 'Page not found' : error.message}</p>

D. <script>
export let error;
export let status;
</script>

<h1>Error {status}</h1>
<p>{status === '404' ? 'Page not found' : error.message}</p>

Solution

1. Step 1: Check how status is used

   Status is a number, so comparing status === 404 is correct.

   <script>
     export let error;
     export let status;
   </script>
   
   <h1>Error {status}</h1>
   <p>{status === 404 ? 'Page not found' : error.message}</p>

   and D do this, but D compares to string '404' which is wrong.

2. Step 2: Check error.message usage

   <script>
     export let error;
     export let status;
   </script>
   
   <h1>Error {status}</h1>
   <p>{status === 404 ? 'Page not found' : error.message}</p>

   uses error.message as fallback, which is correct. Options B and C incorrectly compare error.message to 404, which makes no sense.

3. Step 3: Confirm correct syntax and logic

   <script>
     export let error;
     export let status;
   </script>
   
   <h1>Error {status}</h1>
   <p>{status === 404 ? 'Page not found' : error.message}</p>

   correctly exports both props and uses a ternary to show special message for 404, else shows error.message.

4. Final Answer:

   Option A code correctly handles 404 and other errors -> Option A

5. Quick Check:

   Compare status number, not error.message [OK]

Hint: Compare status number with 404, not error.message [OK]

Common Mistakes:

• Comparing error.message to 404 instead of status
• Comparing status to string '404' instead of number
• Not exporting both status and error props