I like http://www.wearedevelopers.org/. They try to have different topics but last year there were talks mainly about react and state, one angular talk, one redux talk, one about mob-programming and one from a guy who works at github how they work together.
The year before they had a little more diverse topics. maybe this year they'll suprise me with some backend ;) .... so it's not really a frontend conference, but the last two years most of the speaker were mainly talking about frontend applications.
Atul Sharma
Full Stack Developer | Cloud Native Applications
Google developer conferences, Js Conf, Front end trends...