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 - Server vs universal

• form-actions.md - Form handling patterns

• serialization.md - What can/can't serialize

• error-redirect-handling.md - fail/redirect/error

• 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