The simulator loads the ROM using an XmlHttpRequest, so the application must be served up over HTTP.
The package.json can install an HTTP server, just do:
npm install
Download theloop.2.rom into the src directory.
Start the HTTP server
npm start
Point your browser at localhost:8000/src.
Use the cursor keys for the D-pad.
GT1 files can be loaded by starting the Loader and dropping a .gt1 file onto the VGA display from File Explorer or Finder.