If you mean Backbone/Angular/framework of the day, that one is booming. Uploading your CV to one of the popular job boards will get you over 10 calls a day.
1) Household internet giants; i.e Google, Amazon etc
2) Betting/online gaming industry
3) Old Street startups
4) Content delivery; either on device side (set top boxes, consoles etc) or on market side(game, movie, app downloads)
Attending related meetups and handing over a few business cards might do wonders.
disclaimer: I work for Caplin who develops HTML5 financial apps.
The work is very interesting a you are building a huge single page app (not really comparable to most of the "standard" SPAs you encounter in terms of size and complexity) where everything is real-time.