This was a small project I did a few years ago when I was learning about web dev and it includes a few interesting concepts: Loading and displaying tiled maps, collision detection and lag compensation. It's a pretty hacky project and I cringe when I look back at my old code, but maybe it is still helpful for other people.

It also includes a map editor I wrote in Java when I was first learning Java.

You can try a working version of the game out at https://perfectcollisions.herokuapp.com/