<!-- include this library -->
<script src="https://unpkg.com/es-modularize"></script>
<!-- define import maps -->
<script>
  ESModularize.build({
    react: ESModularize.load("https://unpkg.com/react@latest/umd/react.development.js").sync().umd("React"),
    "react-dom": ESModularize.load("https://unpkg.com/react-dom@latest/umd/react-dom.development.js")
      .sync()
      .umd("ReactDOM"),
  });
</script>
<!-- now module imports can work -->
<script type="module" src="entry.js"></script>

<!-- include this library -->
<script src="https://unpkg.com/es-modularize"></script>
<!-- define import maps -->
<script>
  (async () => {
    ESModularize.build({
      react: (await ESModularize.load("https://unpkg.com/react@latest/umd/react.development.js").async()).umd("React"),
      "react-dom": (
        await ESModularize.load("https://unpkg.com/react-dom@latest/umd/react-dom.development.js").async()
      ).umd("ReactDOM"),
    });
    // now module imports can work, but script elements should be created asynchronously.
    document.body.appendChild(Object.assign(document.createElement("script"), { type: "module", src: "entry.js" }));
  })();
</script>