Ask HN: What is the best JavaScript stack for a beginner to learn?

I'm an experienced Rails developer, and I'm helping a friend learn about javascript frameworks so he can eventually get a job (we're kinda learning together). He was considering the MEAN stack, but with the announcement of all the breaking changes in angular 2.0, I don't think it would be a good use of time to learn angular. It would be nice if there was a Rails of javascript, but there seems to be a lot of competing technologies. Obviously, you can learn new things at a new job, but it would still be better to learn something with a lot of adoption. I'm thinking a MEEN stack (using ember instead of angular) or even using react and flux. Meteor is another choice, but I'm not sure how widely adopted it is. I think it would be best for him to pick one stack and master it well before moving on. It's annoying because, when it comes to Rails, I know exactly what skills a beginner needs to learn. Does anyone know what the more successful js bootcamps like h