Magic the Gathering engine written in JS. Kind of a hobby project, maybe will be usable for playing.
MtG engine with rules enforcement. Additional goals: draft engine, modality for embedding in other games (Shandalar-like Ravniсa JS game? Who knows.)
Better understanding of Magic: the Gathering rules.
Experience on prototyping and designing complex Javascript application.
Not yet. Well, you can draw starting hands, put spells on the stack but that's about it.