At least in nw.js which is a similar toolkit to Electron:

{ "name": "helloworld", "main": "index.html" }

And index.html is just whatever HTML web page you want, like "<html><herd><title>Hello World</title></herd><body>Hello World</body></html>". You could also use a javascript file as your "main" file if you want.

Even when you screw up the HTML it will still load, which won't happen if you get your underscores wrong in your example.

Edit: removed erroneous formatting