SvelteKit Server Functions Preprocessor

This is the missing SvelteKit server functions library. (Well, sort of, it's more of a proof of concept. Not production ready.)

A SvelteKit preprocessor that automatically transforms server-side functions into API endpoints, enabling seamless client-server communication in your SvelteKit applications.

async function server_getData(id) {
	// This code runs on the server
	const data = await db.query('SELECT FROM items WHERE id = ?', [id]);
	return data;
}
// Use the function as if it were local
const data = await server_getData(123);

Table of Contents

• Features
• Installation
• Usage
• How It Works
• Function Requirements
• Example
• Security Considerations
• Limitations
• Contributing
• License

Features

• 🚀 Automatically generates API endpoints from server functions
• 🔄 Transforms server function calls into fetch requests
• 🔒 Secure function isolation with unique endpoint paths
• 📦 Zero runtime configuration needed
• 🔍 Intelligent import handling
• ⚡ TypeScript support out of the box - full type safety

Installation

npm install sveltekit-server-functions

Usage

1. Add the preprocessor to your svelte.config.js:

import serverFunctions from 'sveltekit-server-functions';
export default {
	preprocess: [serverFunctions(), vitePreprocess()]
};

2. Create server functions in your Svelte components by prefixing them with server_:

async function server_getData(id) {
	// This code runs on the server
	const data = await db.query('SELECT FROM items WHERE id = ?', [id]);
	return data;
}
// Use the function as if it were local
const data = await server_getData(123);

The preprocessor will automatically:

• Create an API endpoint for the server function
• Transform the function call into a fetch request
• Handle data serialization and error handling

How It Works

1. During build time, the preprocessor scans your Svelte files for functions prefixed with server_
2. For each server function, it:
   • Creates a unique API endpoint in your project's src/routes/api directory
   • Transforms the original function call into a fetch request
   • Preserves all necessary imports and types
3. The generated API endpoints handle:
   • Parameter parsing
   • Response serialization
   • Error handling

Function Requirements

• Must be async functions
• Must be prefixed with server_
• Must be defined in the script section of a Svelte component
• Should return JSON-serializable data

Example

<script>
	import { db } from '$lib/database';

	// Define a server function to create a user
	async function server_createUser(username, email) {
		// This function runs on the server
		const user = await db.users.create({
			username,
			email,
			createdAt: new Date()
		});
		return user; // Return the created user
	}

	// Handle form submission
	async function handleSubmit() {
		try {
			// Call the server function as if it were local
			const newUser = await server_createUser('john_doe', 'john@example.com');
			console.log('User created:', newUser);
		} catch (error) {
			console.error('Failed to create user:', error);
		}
	}
</script>

<!-- Button to trigger user creation -->
<button on:click={handleSubmit}>Create User</button>

Security Considerations

• Server functions are only executed on the server
• API endpoints use unique hashed paths to prevent collisions
• Request validation is automatically handled
• Error messages are sanitized before being sent to the client

Limitations

• Server functions must return JSON-serializable data
• Circular dependencies in server functions are not supported
• Components can only call the server functions that are declared in the same file.

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

MIT License - feel free to use this package in your projects!