Polyfills are not added to the service worker in production

[slavafomin]

Describe the bug

Hello!

I'm using latest Svelte Kit 5 with a service-worker (i.e. a src/service-worker.ts file). I'm also using node polyfills:

// vite.config.ts

export default defineConfig({
  plugins: [
    nodePolyfills({
      include: ['buffer'],
      globals: {
        Buffer: true,
      },
    }),

However, it works fine for my main application, but when it comes to service worker it can't find a Buffer object in runtime.

Also, the service worker works fine during development, but fails in production.

Reproduction

• add vite-plugin-node-polyfills plugin with Buffer polyfill
• try to use Buffer inside the service worker in production (not dev-server)

System Info

System:
    OS: Linux 6.8 Ubuntu 22.04.5 LTS 22.04.5 LTS (Jammy Jellyfish)
  Binaries:
    Node: 22.16.0 - ~/.nvm/versions/node/v22.16.0/bin/node
    npm: 11.4.2 - ~/.nvm/versions/node/v22.16.0/bin/npm
    pnpm: 10.10.0 - ~/.nvm/versions/node/v22.16.0/bin/pnpm
  Browsers:
    Chromium: 137.0.7151.103
  npmPackages:
    @sveltejs/adapter-static: ^3.0.8 => 3.0.8 
    @sveltejs/kit: ^2.21.5 => 2.21.5 
    @sveltejs/vite-plugin-svelte: ^5.1.0 => 5.1.0 
    svelte: ^5.34.4 => 5.34.4 
    vite: ^6.3.5 => 6.3.5
    vite-plugin-node-polyfills: ^0.23.0 => 0.23.0

Severity

Blocking app's release

[slavafomin]

Also, if I look inside the generated bundle (service-worker.js) I can see the code of the Buffer polyfill:

But in the browser I'm still getting the: Buffer is not defined error.

[dummdidumm]

Right now the service worker is an entirely separate build and so it doesn't pick up config like this I believe.
With vite environment API and us adjusting SvelteKit's Vite plugin accordingly this issue should go away