Untitled

<!DOCTYPE html>
<html>

  <head>
  </head>

  <body>
    <script type="module" src="./script.js"></script>
  </body>

</html>

(async () => {
    const {default: MyClass} = await import("./MyClass.js");
    let c = new MyClass();
    // ...
})()
.catch(error => {
    // Handle/report error
    console.error(error);
});

export default class MyClass {
    constructor() {
        const p = document.createElement("p");
        p.appendChild(document.createTextNode("MyClass okay!"));
        document.body.appendChild(p);
    }
}