sveltekit-data-flow

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.

```typescript

// +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');

},

};

```

• [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

• 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