Nice one! I like the idea of where it's going. It's not everyday that I see a jam entry entirely made in JS :D
It does get repetitive after a couple of shots though. I'm sure that if you were to add more enemy types and more guns / ways to get rid of them, this could be quite an interesting game!
Congrats on submitting your entry an hour before the deadline! You can come try out mine if you wish, have fun multitasking! xD