Most of the time I saw it as a tool to use, when CSS wasn't powerfull enough.
After using NodeJS I was blewn away. NPM alone was a killer feature PHP was missing.
Functions as objects that can be passed around and closures introduced me to functional programming.
I really thought PHP would go downhill after I saw the whole JavaScript hype and switched 100% away from PHP. Many web-companies here in Germany were just doing Java or PHP at that time (before 2010) and if you didn't know about one of those two languages you were screwed, but now I do 100% JavaScript development AND get better projects than with PHP. But I have to admit Facebook pumping money into PHP helped tremendously to make it better.
At the moment I have smaller WOW-moments with TypeScript, RxJS and NixOS. Smaller basically because I don't have work-related projects at the moment to use them, but they seem to fix a few pain points I had with JavaScript, React/Redux and Vagrant. (undefineds everywhere, realtime-data stream control and sane dependency management)