I would like to know that too.
I saw there's a nodejs package but it's not documented at all
https://github.com/bitshares/bitsharesjs

I'm using get_order_book() to get orderbook,
is there a way to let websocket api notice me when one item in orderbook changed ?

I see there is a subscribe_to_market(), though I'm still don't know what id does, but it is not like notice for orderbook.

what is the best way to do this ?