index.html tags

Would it be possible to change the meta tags of the index.html before it's parsed for say its preview used by scrapers?

Basically non static webpage/game that can have a meta to match.

Which tags do you want to be able to change specifically?

It's usually it's done in php, and I know it would be a stretch to get it to work properly with javascript, but an example is like when you post a url to sites like Facebook, and Twitter those sites parse the urls and get tags such as title, and even image previews to give the user a better idea of what the link is about.

Of course another question would be if it should even be in the index.html, as many games are hosted in other pages.

Ah, you mean all the social media tags? That would be an interesting thing to cover.