astro/packages/integrations/lit/server-shim.js

import { installWindowOnGlobal } from '@lit-labs/ssr/lib/dom-shim.js';

if (typeof fetch === 'function') {
	const _fetch = fetch;
	installWindowOnGlobal();
	globalThis.fetch = window.fetch = _fetch;
} else {
	installWindowOnGlobal();
}

window.global = window;
document.getElementsByTagName = () => [];
// See https://github.com/lit/lit/issues/2393
document.currentScript = null;

const ceDefine = customElements.define;
customElements.define = function (tagName, Ctr) {
	Ctr[Symbol.for('tagName')] = tagName;
	return ceDefine.call(this, tagName, Ctr);
};