Lit SSR doesn't work in worker-like environments. e.g. Cloudflare Workers and Vercel Edge.

npm install
npm run dev

You'll get Uncaught ReferenceError: window is not defined.

npm run build

Build the bundle and inspect there's window in the output code. (dist/index.js - I git committed this to show it easily)

!! NPM only !!

npm run patch

This will patch lit-html and @lit/reactive-element package.json to create a exports worker condition that's the same as the node condition.

npm run unpatch

Undo the above if needed.