With the following example code:

import * as React from "react";
import { render } from "react-dom";

const App = () => {
  return (
    <React.StrictMode>
      <div>Hello</div>
    </React.StrictMode>
  );
};

render(<App />, document.getElementById("root"));


If you move to the live with the <div> and call M-x comment-line, the
line is commented out with two forward slashes, instead of the proper

{{/* <div>Hello</div> */}}

In GNU Emacs 27.0.91 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.20)
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: NixOS 20.09 (Nightingale)