Layout load functions in Svelte - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a layout load function in SvelteKit?

A layout load function runs before the page loads and fetches data or performs setup for all pages using that layout. It helps share data or logic across multiple pages.

beginner

Where do you define a layout load function in SvelteKit?

You define it in a +layout.js or +layout.ts file inside the folder where the layout is used. This function exports a load() that runs before the layout renders.

intermediate

How does a layout load function share data with pages?

The layout load function returns an object with data. This data is accessible in the layout and all child pages via the special $page.data store or props.

intermediate

Can a layout load function run on the server, client, or both?

Layout load functions run on the server during initial page load and on the client during navigation. This ensures data is fresh and consistent.

advanced

What happens if a layout load function throws an error?

If a layout load function throws an error, SvelteKit shows an error page or you can handle it with an error boundary layout. This prevents broken pages.

Where do you place a layout load function in SvelteKit?

A In a +layout.js or +layout.ts file

B In a +page.js file

C In the main.js file

D Inside the component script tag

Layout load functions belong in +layout.js or +layout.ts files to run before layouts render.

What does a layout load function return?

A A boolean value

B A string with HTML

C An object with data to share

D Nothing

It returns an object containing data that layouts and pages can use.

When does a layout load function run?

A Only on the server

B Only during build time

C Only on the client

D On server load and client navigation

Layout load functions run on the server initially and on the client during navigation.

How can pages access data from a layout load function?

A Using $page.data store or props

B By importing the layout file

C Using global variables

D They cannot access it

Pages access layout data through the $page.data store or props passed down.

What happens if a layout load function fails with an error?

A The app crashes without message

B SvelteKit shows an error page or error boundary

C The error is ignored

D The page reloads automatically

SvelteKit shows an error page or uses error boundaries to handle load function errors gracefully.

Explain how a layout load function works in SvelteKit and why it is useful.

Think about how you prepare shared data for multiple pages.

Describe where and how you define a layout load function and how pages access its data.

Consider the file structure and data flow.

Practice

1. What is the main purpose of a load function in a Svelte layout?

easy

A. To style the layout component with CSS

B. To fetch or prepare data before the layout renders

C. To handle user events like clicks

D. To define routes for the application

Solution

1. Step 1: Understand the role of load functions in Svelte layouts

   Load functions run before the layout renders to get data ready.

2. Step 2: Identify what load functions do

   They fetch or prepare data so the layout can use it immediately.

3. Final Answer:

   To fetch or prepare data before the layout renders -> Option B

4. Quick Check:

   Layout load = fetch data before render [OK]

Hint: Load functions prepare data before layout shows [OK]

Common Mistakes:

• Confusing load with styling or event handling
• Thinking load defines routes
• Assuming load runs after layout renders

2. Which of the following is the correct syntax for a layout load function in SvelteKit?

easy

A. export async function load() { return { user: 'Alice' }; }

B. export async function load() { return { props: { user: 'Alice' } }; }

C. export function load() { return { props: { user: 'Alice' } }; }

D. function load() { return { user: 'Alice' }; }

Solution

1. Step 1: Recall the modern SvelteKit load function syntax

   Load functions are async and return data directly, not inside a props object.

2. Step 2: Check each option's return value

   export async function load() { return { user: 'Alice' }; } returns { user: 'Alice' } directly, which is correct for layout load.

3. Final Answer:

   export async function load() { return { user: 'Alice' }; } -> Option A

4. Quick Check:

   Load returns data directly, no props wrapper [OK]

Hint: Load returns data directly, no props wrapper [OK]

Common Mistakes:

• Returning data inside a props object (old pattern)
• Missing async keyword
• Not exporting the load function

3. Given this layout load function:

export async function load() {
  return { user: 'Bob', theme: 'dark' };
}

What data will be available in the layout component's data prop?

medium

A. { user: 'Bob', theme: 'dark' }

B. { props: { user: 'Bob', theme: 'dark' } }

C. undefined

D. { user: 'Bob' }

Solution

1. Step 1: Understand what the load function returns

   The load function returns an object with keys user and theme.

2. Step 2: Know how layout receives load data

   The layout component receives the returned object as its data prop directly.

3. Final Answer:

   { user: 'Bob', theme: 'dark' } -> Option A

4. Quick Check:

   Load return = layout data prop [OK]

Hint: Layout data matches load return object exactly [OK]

Common Mistakes:

• Expecting data inside a props object
• Assuming data is undefined without explicit props
• Only partial data returned

4. Identify the error in this layout load function:

export function load() {
  const user = fetch('/api/user');
  return { user };
}

medium

A. load function should not return any value

B. Returning user inside an object is incorrect

C. fetch should not be used in load functions

D. Missing async keyword and await for fetch

Solution

1. Step 1: Check if fetch is awaited

   fetch returns a promise, so it must be awaited inside an async function.

2. Step 2: Verify load function declaration

   load must be async to use await; here it is missing async.

3. Final Answer:

   Missing async keyword and await for fetch -> Option D

4. Quick Check:

   Async + await needed for fetch in load [OK]

Hint: Always use async and await with fetch in load [OK]

Common Mistakes:

• Forgetting async keyword
• Not awaiting fetch promise
• Returning unresolved promise instead of data

5. You want to share user info fetched in a layout load function with all nested pages. Which approach correctly achieves this in SvelteKit?

hard

A. Store user data in a global variable outside load functions

B. Fetch user data separately in each page's load function

C. Use a layout load function that fetches user data and returns it; nested pages access via data

D. Pass user data as props manually from layout to pages

Solution

1. Step 1: Understand data flow in SvelteKit layouts

   Layout load functions run once and share data with nested pages via the data prop.

2. Step 2: Identify best practice for shared data

   Fetching user data in layout load and returning it allows nested pages to access it automatically.

3. Final Answer:

   Use a layout load function that fetches user data and returns it; nested pages access via data -> Option C

4. Quick Check:

   Layout load shares data with nested pages [OK]

Hint: Fetch once in layout load to share data with pages [OK]

Common Mistakes:

• Fetching data repeatedly in each page
• Using global variables causing stale data
• Manually passing props instead of using data prop