1. Rails was a breath of fresh air over the explicit-rather-than-implicit web frameworks of the time, but while making a splash in the startup world, it didn't seem to be embraced in legacy bigcorp settings.
2. JS is an ecosystem that is mandatory on the frontend and has become viable (and actually novel) on the backend, and was eventually able to make inroads in bigcorp settings unlike Ruby. This ubiquity and agreeableness, combined with its rich array of libraries and active community, makes it compelling. As the Ruby community matured, the hype around it has died down, leading to less buzz but also less prominent innovation.
3. React Native is the killer SDK for making one codebase work on every relevant (mobile) platform. (Presumably, if the author were concerned with lives-on-desktop applications too, Electron would be mentioned as well.)
4. The core JS language is actually being worked on now and isn't nearly as quasi-abandonware or as horrendous as it once used to be. (Some credit paid to browser-makers is missing, as every browser-maker has done their part in both trying to move the ecosystem forward in divergent ways, and then much later coming together to harmonize their implementations and resolve to work in a more coordinated way. This 10-year evolution ultimately made duct tape shims like jQuery unnecessary, which paved the way for more holistic frameworks like Ember, Knockout, Angular, and React to set a different architectural model for JS code, landing the community where it is today.)