See https://github.com/jacob-ebey/react-router-runtime-prerender

prerender.ts

import * as fsp from "node:fs/promises";
import * as path from "node:path";
import { createRequestHandler } from "react-router";
import * as build from "virtual:react-router/server-build";

const MAGIC_BASE_URL = build.basename;
const TRUE_BASE_URL = process.env.BASE_URL ?? "/";

const PRERENDER_PATHS = [`${MAGIC_BASE_URL}`, `${MAGIC_BASE_URL}parent/about/`];

const DATA_HEADER = "X-React-Router-Prerender-Data";
process.env.IS_RR_BUILD_REQUEST = "yes";

const handler = createRequestHandler(build, "production");

const clientPath = path.join("./build", "client");
const assetsPath = path.join(clientPath, "assets");

/**
 * Substitute the magic placeholder base URL with the expected one
 */
const rewriteContent = (content: string): string => {
  return content.replaceAll(MAGIC_BASE_URL, TRUE_BASE_URL);
};

const rewriteAssets = async () => {
  for await (const entry of fsp.glob(["**/*.js", "**/*.html", "**/*.css"], {
    cwd: assetsPath,
  })) {
    const assetPath = path.join(assetsPath, entry);
    const source = await fsp.readFile(assetPath, { encoding: "utf-8" });
    await fsp.writeFile(assetPath, rewriteContent(source), {
      encoding: "utf-8",
    });
    console.log(entry);
  }
};

const renderRoute = async (prerenderPath: string) => {
  // You can do things concurrnetly if you'd like
  let dataRequestPath = prerenderPath.endsWith("/")
    ? `${prerenderPath}_.data`
    : `${prerenderPath}.data`;
  const dataURL = new URL(dataRequestPath, "http://pre.render");
  const dataResponse = await handler(new Request(dataURL));
  const data = await dataResponse.text();

  if (!dataResponse.ok) {
    throw new Error(
      `Invalid data response for ${prerenderPath}: ${dataResponse.status}`,
    );
  }

  const htmlURL = new URL(prerenderPath, "http://pre.render");
  const htmlResponse = await handler(
    new Request(htmlURL, {
      headers: {
        [DATA_HEADER]: data,
      },
    }),
  );
  const html = await htmlResponse.text();

  if (!htmlResponse.ok) {
    throw new Error(
      `Invalid html response for ${prerenderPath}: ${dataResponse.status}`,
    );
  }

  if (!prerenderPath.startsWith(MAGIC_BASE_URL)) {
    throw new Error(
      "Invalid prerender path: expected URL to start with (magic) base URL",
    );
  }
  // Drop /foo of /foo/ → /
  const destPrerenderPath = prerenderPath.slice(MAGIC_BASE_URL.length - 1);
  const htmlFilepath = path.resolve(
    path.join(
      clientPath,
      ...(destPrerenderPath + "/index.html").split("/").filter(Boolean),
    ),
  );

  await fsp.mkdir(path.dirname(htmlFilepath), { recursive: true });
  await fsp.writeFile(htmlFilepath, rewriteContent(html), "utf-8");
};

await Promise.all([
  ...PRERENDER_PATHS.map((p) => renderRoute(p)),
  rewriteAssets(),
]);