@openworkers/adapter-sveltekit

SvelteKit 2 and 3 adapter for OpenWorkers. Requires OpenWorkers runner 0.15.21 or later, 1.x included.

Installation

bun add -d @openworkers/adapter-sveltekit

Usage

SvelteKit 3

// vite.config.js
import { defineConfig } from 'vite';
import { sveltekit } from '@sveltejs/kit/vite';
import adapter from '@openworkers/adapter-sveltekit';

export default defineConfig({
  plugins: [sveltekit({ adapter: adapter({ outDir: 'build' }) })]
});

SvelteKit 3 builds a single worker for SSR and API routes. If functions: true is set, the adapter emits a warning and builds a single worker. It does not generate a functions/ directory; _routes.json contains an empty functions list.

SvelteKit 2

// svelte.config.js
import adapter from '@openworkers/adapter-sveltekit';

export default {
  kit: {
    adapter: adapter({
      outDir: 'build', // Output directory (default: 'build')
      functions: true // Generate mini-workers for API routes (default: false)
    })
  }
};

Options

Option	Type	Default	Description
outDir	string	'build'	Output directory for the build
functions	boolean	false	Generate mini-workers on SvelteKit 2; warn and ignore on SvelteKit 3
nodeCompat	boolean	false	Include shims for Node.js built-in modules

Output

build/
├── _worker.js     # Main SSR worker
├── _routes.json   # Route manifest for edge routing
├── assets/        # Static assets and prerendered pages
└── functions/     # Mini-workers for API routes (if functions: true)
    ├── api-hello.js
    └── api-users.js

Functions Mode

On SvelteKit 2, when functions: true, the adapter generates a separate mini-worker for each +server.ts endpoint:

• /api/hello/+server.ts → functions/api-hello.js
• /api/users/+server.ts → functions/api-users.js

The route mappings are included in _routes.json:

{
  "functions": [
    { "pattern": "/api/hello", "worker": "functions/api-hello.js" },
    { "pattern": "/api/users", "worker": "functions/api-users.js" }
  ]
}

This prepares for native project routing in the OpenWorkers runner, where each function can be deployed as a separate worker for better isolation and scaling.

TypeScript

For proper types on platform.env, add @openworkers/workers-types:

bun add -d @openworkers/workers-types

Then in src/app.d.ts:

/// <reference types="@openworkers/workers-types" />

declare global {
  namespace App {
    interface Platform {
      env: {
        KV: BindingKV;
        ASSETS: BindingAssets;
      };
    }
  }
}

export {};

Deployment

Build your SvelteKit app, then deploy it with the OpenWorkers CLI:

# Build
bun run build

# Deploy
ow workers upload my-app ./build

For a first deployment, you'll need to set up the worker and its assets binding:

# Create the worker
ow workers create my-app -d "My SvelteKit App"

# Create a storage bucket for static assets
ow storage create my-storage

# Create an environment and bind the storage as ASSETS
ow env create my-app-env
ow env bind my-app-env ASSETS my-storage --type assets

# Link the environment to the worker
ow workers link my-app my-app-env
# Build and upload
bun run build
ow workers upload my-app ./build

Examples

• world-time-app — SSR-rendered clocks with server-side positioned hands
• httpbin — HTTP request testing tool
• rock-paper-scissors — Provably fair Rock Paper Scissors game

License

MIT

Development

Use Node 22.17 or later for the SvelteKit 3 fixture builds.

bun install --frozen-lockfile
bun install --cwd test/fixtures/kit3 --frozen-lockfile
bun run build
bun run check
bun test

The compatibility tests build real SvelteKit 2 and 3 apps, then exercise the bundled worker with SSR, hooks, bindings, cookies, form actions, streaming, page data, static assets and prerendered pages. They also check a URL base path and the SvelteKit 3 functions warning. SvelteKit 3 fixture dependencies have a separate lockfile so the adapter's SvelteKit 2 build stays independent.