This is a free game engine developed for programming browser based games. It uses the Javascript language and CSS to dress up the page. They run pretty reliably together. Use this engine to create your own game. This project is intended for beginners, wanting to learn how to program video games. Better if you're a web designer that knows some CSS.
This engine uses threads for animation by looping through frames, each frame being a single thread of execution, enabling us to have more control over animation. Therefore we can coordinating two entities running independently to lock them both by their id's. For example, a character can block a punch from another character, which "locks" in place independent frames from two mutual entities running concurrently in their own time zones, by using their thread id's. There we can invoke instance() function to inject additional algorithm before having the two halted threads (or the entire game) to proceed.
Javascript is event driven so you can program images to move across the screen just by changing the coordinates, x and y and the browser will do this for us. On our part we're just basically changing the CSS stuff like top:1px; and left:1px; with position:absolute;
That's how it's done mainly, but this engine coordinates threaded animation frames along with the speed of coordinates changing.
Background and foreground and character overlaps are managed by setting z-index.