Next Steps and Component Libraries

Now that you’ve mastered Svelte 5 runes, snippets, actions, and advanced transitions, the next horizon is packaging reusable component libraries and integrating full-stack capabilities.

1. Packaging Libraries with @sveltejs/package

To build an npm-ready component library, Svelte provides @sveltejs/package. It extracts TypeScript definitions (.d.ts), processes styles, and emits clean ES modules:

# Generate dist packages from src/lib
npx svelte-package

Ensure your package.json specifies proper exports:

{
	"name": "my-svelte-ui",
	"type": "module",
	"exports": {
		".": {
			"types": "./dist/index.d.ts",
			"svelte": "./dist/index.js",
			"default": "./dist/index.js"
		}
	}
}

2. Testing Svelte 5 Components

Use Vitest with @testing-library/svelte for component testing:

// Button.test.ts
import { render, fireEvent } from '@testing-library/svelte';
import Button from './Button.svelte';
import { describe, it, expect, vi } from 'vitest';
 
describe('Button', () => {
	it('fires onclick handler when clicked', async () => {
		const handleClick = vi.fn();
		const { getByRole } = render(Button, { props: { onclick: handleClick } });
 
		const button = getByRole('button');
		await fireEvent.click(button);
 
		expect(handleClick).toHaveBeenCalledTimes(1);
	});
});

3. Ready for Full-Stack?

Continue your journey in Track 3: Basic SvelteKit to master file-based routing, server data loaders, secure cookie handling, form actions, and API endpoints!