@thomasfosterau/effect-sveltekit

Effect v4-native integration for SvelteKit: write load functions, form actions, endpoints, hooks, and remote functions as Effects; move custom types across the server/client boundary with Effect Schema; and deploy on an Effect HTTP server.

Part of the effect-svelte monorepo. Depends on @thomasfosterau/effect-svelte for the Svelte runes hooks.

Installation

npm install @thomasfosterau/effect-sveltekit effect@beta svelte @sveltejs/kit
# the Effect deployment adapter additionally needs:
npm install @effect/platform-node@beta

Entry points

| Import | What it provides | | ---------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | @thomasfosterau/effect-sveltekit | universal helpers (load, the Remote call namespace, transport, sveltekitConfig, reroute) | | …/server | server wrappers (serverLoad, action, actions, handle, endpoint), app runtimes (makeServerRuntime / makeUniversalRuntime), the per-request runtime seam (makeRuntimeAdapter / RequestRuntime), RemoteFunction | | …/client | browser-only Navigation / State / Remote namespaces and useRemoteQuery | | …/vite | the effectKit() Vite plugin (auto-wrap bare-Effect route exports) | | …/adapter | the Effect HTTP deployment adapter |

Example

// vite.config.ts — return Effects directly from route files
import { sveltekit } from "@sveltejs/kit/vite";
import { effectKit } from "@thomasfosterau/effect-sveltekit/vite";

export default { plugins: [effectKit(), sveltekit()] };

// +page.server.ts
import { Effect } from "effect";
export const load = (event) => Effect.succeed({ id: event.params.id });

What's included

• Effects as route exports — explicit wrappers, app-wide runtimes (services built once per process), or the effectKit() plugin.
• Bring-your-own per-request runtime — makeRuntimeAdapter(provider, opts) binds the server wrappers to a RequestRuntime provider, so the handler effect's services are your own application catalogue (not SvelteKitServices). Adopt a runtime the consumer stashed on event.locals (RequestRuntime.fromLocals, resolved per call so a mid-request rebuild is honoured), let the package build + dispose one per request (RequestRuntime.fromLayerPerRequest, with afterResponse to route disposal through Cloudflare Workers' ctx.waitUntil), or reuse the build-once model (fromManagedRuntime / fromLayer). RemoteFunction.withRuntime(provider) gives remote functions the same seam.
• Pluggable boundary error translation — pass translateError to makeRuntimeAdapter, makeServerRuntime, or RemoteFunction.withRuntime to map a failed Cause to SvelteKit control flow (error(404), redirect(), remote-form invalid()) instead of a generic 500.
• Remote functions — define with RemoteFunction.* (a bare Effect Schema validator is accepted and auto-wrapped), consume via the Remote namespace (Remote.callQuery, Remote.liveQueryStream, …); useRemoteQuery bridges a reactive remote resource to an AsyncResult. RemoteFunction.withRuntime also takes a formError hook to map a domain error into SvelteKit field issues.
• transport ⇄ Effect Schema (Hooks.transport / transporter, plus Hooks.markerTransporter for non-round-tripping wrappers) and $env ⇄ Effect Config.
• Client navigation/state — the Navigation (goto/invalidate/… plus beforeNavigate/afterNavigate/onNavigate streams) and State (page) namespaces.
• Effect deployment adapter — the generated app is a platform-neutral Effect HttpApp (makeHandlerWith): serve it as a production Node HTTP server (effect/unstable/http + @effect/platform-node, the default) or as a Web fetch handler on Cloudflare Workers (effectAdapter({ target: "fetch" }) / toWebHandler). Asset serving is a pluggable AssetSource (AssetSource.fileSystem for Node, AssetSource.cloudflareAssets(env.ASSETS) for Workers, or any custom source — R2, KV, a CDN passthrough).

See the monorepo README for the full API and a runnable SvelteKit example.

License

MIT