In SvelteKit, hooks are special functions that allow you to run custom logic at specific points during the lifecycle of a request. They enable you to modify the behavior of your application globally. SvelteKit currently provides two main hooks: handle and handleError.

1. handle: This hook allows you to modify the request and response objects before they reach your SvelteKit endpoints or pages. It’s useful for implementing middleware-like functionality, such as authentication, logging, or custom headers.

   Example:

   // src/hooks.server.ts
   
   import type { Handle } from '@sveltejs/kit';
   
   export const handle: Handle = async ({ event, resolve }) => {
       // Do something with the request (event)
   
       // You can modify the response by passing it to resolve
       const response = await resolve(event);
   
       // Do something with the response
   
       return response;
   };

2. handleError: This hook is used to handle errors that occur during the request lifecycle. It allows you to log errors, customize error responses, or perform other error handling tasks.

   Example:

   // src/hooks.server.ts
   
   import type { HandleError } from '@sveltejs/kit';
   
   export const handleError: HandleError = ({ error, event }) => {
       // Log the error
       console.error(error);
   
       // Customize the error response
       return {
           message: 'An unexpected error occurred.',
           code: error.code || 'UNKNOWN'
       };
   };

Table of Contents

Use Cases for Hooks

• Authentication: Check if a user is authenticated before allowing access to certain pages or endpoints.
• Logging: Log requests and responses for debugging or analytics purposes.
• Custom Headers: Add or modify headers for all responses.
• Error Handling: Customize the way errors are handled and reported.

Hooks in SvelteKit provide a powerful way to implement cross-cutting concerns and global behaviors in your application, making it easier to maintain and extend.