astro/packages/renderers/renderer-preact/server.js

import { h, Component as BaseComponent } from 'preact';
import render from 'preact-render-to-string';
import StaticHtml from './static-html.js';

function check(Component, props, children) {
  if (typeof Component !== 'function') return false;

  if (Component.prototype != null && typeof Component.prototype.render === 'function') {
    return BaseComponent.isPrototypeOf(Component);
  }

  const { html } = renderToStaticMarkup(Component, props, children);

  if (typeof html !== 'string') {
    return false;
  }

  // There are edge cases (SolidJS) where Preact *might* render a string,
  // but components would be <undefined></undefined>

  return !/\<undefined\>/.test(html);
}

function renderToStaticMarkup(Component, props, children) {
  const html = render(h(Component, { ...props, children: h(StaticHtml, { value: children }), innerHTML: children }));
  return { html };
}

export default {
  check,
  renderToStaticMarkup,
};