I'll start with WebGL2Fundamentals and WebGPU Fundamentals: both GREAT resources for learning WebGL, WebGL2 and WebGPU. Filled with well-written explanations and interactive demos. I've learned a lot from it.
Then we have Muhammad's Behind the Pretty Frames. He explains in amazing detail how the beautiful graphics of modern, popular games —such as Resident Evil 2, and 3 remakes— are achieved.
Pathfinding Visualizer is a simple but awesome tool to understand, visually, how 4 different path finding algorithms work: Breadth-First Search, Depth First, Dijkstra and A-Star.
The Book of Shaders is something I've seen recommended here and there, although I haven't had the chance to dig into it myself, yet.
Shadertoy is a place were people share —you guessed it— shaders. They run in the browser thanks to the magic of WebGL, so you don't need to sign up or install anything. Just open one and see it running, along with its source code.
Tixi Land and Sliderland are two fun toys that give you some basic JavaScript functionality for you to write a simple function (in 32 characters or fewer in the case of Tixi) to render a 16x16 dot array, in Tixi, or to 64 HTML sliders, in Sliderland.
Crocodile3D is a very ingenious game-development application. It seems similar to RPG Maker, but in 3D. Basically you get to do 3D games with 2D tilesets — which makes it very friendly to people with zero programming experience, and very quick to get something up and running. Take a look at the intro video in the home page — it's about 3 minutes long and showcases it perfectly. It has a free downloadable demo. And it's available for Windows, MacOS and Linux!
js13kGames is a JavaScript coding competition for HTML5 Game Developers running yearly since 2012. All submissions are limited in file size to 13 kilobytes. Each year has a theme. The theme for 2022 was death. Some pretty mind-blowing things come out of it.
Lurum Dare is another game development competition. This one isn't restricted to JavaScript. Participants must complete a game from scratch in 72hs.
melonJS is an open source HTML5 2D game engine. Check out the made-with-melonJS gallery.
strudel is a live coding platform to write dynamic music pieces in the browser.
dwitter.net is "a challenge to see what awesomeness you can create when limited to only 140 characters of javascript and a canvas". People create some pretty wild and beautiful animations I could have never imaged could be done in less than 140 chars of JS! The best authors I've seen so far are KilledByAPixel and Rodrigo Siqueira. Some of my fave dweets: Lava Cave, Sierpiński Mountains, Wolfendweet (this one is actually interactive! WTF!), Treescape, City Blocks, Seasons Dweetings, Pseudo Global illumination, Construction #1, Construction #2, White roots and Sailing in rough sea, an unnamed square spiral (lots of more cool stuff in that chain of remixes!) and this awesome nebulous gradient effect.