I don't 100% know in the case of triplit, but pouchdb does what you describe for "free" (i.e. you don't need to code it). firebase uses a websocket, pouch uses

I don't 100% know in the case of triplit, but pouchdb does what you describe for "free" (i.e. you don't need to code it). firebase uses a websocket, pouch uses (I believe) long polling.