I know it's been popular for a few years but I'm still incredibly excited by Node.js . I'm also excited about Electron and some of the stuff Mozilla is doing, like Tofino. React is being used in Mozilla's Dev Tools and Tofino, so I'm exciting about that as well. I had a blast working on Firefox OS for TV -- I'm super into alternative use cases for JavaScript. In short, there's too much out there to keep up!