Many of the Wii U's greatest games have long since been ported over to Switch. It's just something that we have all come to accept with the console — yes, it had some great games, but most of them are now playable elsewhere (often in a better condition).
We expect to see these games playing today on the Switch, or maybe even on the 3DS a few years back, but we weren't anticipating that you would be able to play certain titles via a web browser. Well, that's exactly what one player, @JasperRLZ (primary coder of noclip), has managed to do.
Discovering that the Wii U edition of Mario vs. Donkey Kong: Tipping Stars was written in HTML and JavaScript (yep, who knew?), Jasper worked out that with 1,400 lines of shim code (which is used to change the behaviour of the pre-existing code, we learnt), the game could make the leap over to a browser — Chrome in this instance.
Having got the game up and running, the player shared the results of their code tweaks in the following video on Twitter:
It seems that the reason that the game was written in HTML and JavaScript was as a demonstration of the Nintendo Web Framework — a discontinued system designed to make Wii U game development easier. This was initially used on console apps like Wii Street U and later on some fully fledged games (though none were quite as high profile as Tipping Stars).
It's also worth bearing in mind that Tipping Stars was a cross-platform release with the 3DS, with each version of the game coming with a download code for other on purchase. This may well be another reason for the game being written in HTML so as to more easily allow it to function between the two consoles.
As outlined in the above tweet, the game's code did have some elements specific to the Wii U, but it is apparent that there was not too much so as to make the browser transfer impossible. Of course, the precise method of how to tweak the game as seen above has not been publicly shared (we wouldn't imagine that Nintendo would be best pleased to have it out there), but seeing that it's possible is pretty cool all the same.