nice bomberman clone! one issue i had is that in firefox atleast, spacebar by default scrolls the page. so everytime i drop a bomb the page scrolls, moving the game out of view. you could probably avoid this by calling preventDefault() on the keydown event if the key is spacebar. i got around it by deleting every  element on the page besides the game so the whole page fit inside a single screen height so there was nowhere to scroll. that being said, this brought me back to being a kid, sitting in the middle of the floor playing bomberman on my NES.  nice job!