sveltekit-data-flow

SvelteKit Data Flow

Quick Start

Environment variables: Prefer explicit env vars (src/env.ts + $app/env/private|public) when the experimental flag is enabled.

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 ({ 

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
• explicit-environment-variables.md - typed, validated env vars

Notes

• Server load → universal load via data param | ALWAYS throw redirect()/error()
• No class instances/functions from server load (not serializable)
• $app/env/private is server-only; only mark genuinely safe values as public
• Last verified: 2026-06-08