A long time ago I wrote a platform engine using JavaScript. This was back when I wasn’t so experienced, so it’s not as clean and doesn’t use as good programming practices as it should do.
It is however, fully commented for your viewing pleasure.
Demo 1 – Basic engine, I made it with focus on accuracy. Your red unit should be able to move around very perfectly according to the tile map, and fit neatly into where it should fit, without effort. Use the Arrow Keys to move around. Should work in at least Firefox and Chrome.
Demo 2 – Upgraded the engine with animated sprites, borrowed from Zelda 2. Also added a very primitive AI to make them move. Use the Arrow Keys to move around. Should work in at least Firefox and Chrome.