Doesn’t look like I can try this out. Couldn’t find a link to the game.
They link to it towards the end of the whole thing. But they just decided to make a single word link that doesn’t really suggest that’s where the game is.
https://d07riv.github.io/diabloweb/
So there you go. That’s where you can actaully play diablo 1 in your browser, at least the shareware version unless you have the original mpq file.
I saw this on Redit the other day and as Fraggles has a link to another github repro that gives that link.
It’s pretty cool to play it in the browser! Very tempted to get my copy of D1 and get the MPQ file so I can play it. But it’s pretty big game so only worth if I accualy want to play it all.
grr It’s annoying when a page makes the link so hard to find. Thank you! 
Update: So thanks to Fraggles I manage to give the game a shot. It’s so darn pretty and smooth! I can see why someone called Book of Demons a love letter to the game. Also, that person was right - the free of movement in this in comparison to the newer game is so much easier! In both you can get a ton of enemies coming at you all at once and position helps a ton, but in BoD, you can only ever move along the pathways. It’s not unplayable but does up the difficulty quit a bit.
Still, both are awesome for short bursts of gameplay, so it’s all good. ^^