sveltekit-data-flow

SvelteKit Data Flow

Quick Start

Which file? Server-only (DB/secrets): +page.server.ts | Universal (runs both): +page.ts | API: +server.ts

Load decision: Need server resources? → server load | Need client APIs? → universal load

Form actions: Always +page.server.ts. Return fail() for errors, throw redirect() to navigate, throw error() for failures.

Example

// +page.server.ts
import { fail, redirect } from '@sveltejs/kit';

export const load = async ({ locals }) => { const user = await db.users.get(locals.userId); return { user }; // Must be JSON-serializable };

export const actions = { default: async ({ request }) => { const data = await request.formData(); const email = data.get('email');

	if (!email) return fail(400, { email, missing: true });

	await updateEmail(email);
	throw redirect(303, '/success');
},

};

## Reference Files

- [load-functions.md](references/load-functions.md) - Server vs
  universal
- [form-actions.md](references/form-actions.md) - Form handling
  patterns
- [serialization.md](references/serialization.md) - What can/can't
  serialize
- [error-redirect-handling.md](references/error-redirect-handling.md) -
  fail/redirect/error
- [client-auth-invalidation.md](references/client-auth-invalidation.md) -
  invalidateAll() after client-side auth

## Notes

- Server load → universal load via `data` param | ALWAYS
  `throw redirect()/error()`
- No class instances/functions from server load (not serializable)
- **Last verified:** 2025-01-11

<!--
PROGRESSIVE DISCLOSURE GUIDELINES:
- Keep this file ~50 lines total (max ~150 lines)
- Use 1-2 code blocks only (recommend 1)
- Keep description <200 chars for Level 1 efficiency
- Move detailed docs to references/ for Level 3 loading
- This is Level 2 - quick reference ONLY, not a manual

LLM WORKFLOW (when editing this file):
1. Write/edit SKILL.md
2. Format (if formatter available)
3. Run: npx skills add . --list
4. If the skill is not discovered, check SKILL.md frontmatter formatting
5. Validate again to confirm
-->