That's a great idea. (Un)fortunately it's all client-side.

Guessing you could probably put everything into a redis instance and just hincrby/incr for either the individual queries ie "902", "9021", "90210."

Not sure what would be more performant, REST or a websocket. Not doing anything would be the fastest, though!

http://redis.io/commands/HINCRBY

A Google Analytics tracking of the events would be just fine for this goal.

Oh, great idea! I've never dived (dove??) into event tracking. Is something like this what I want?

    ga('send', 'event', 'input', 'search', 'zip', zipCode);

That will do the trick!