Especially, if you are a student and trying to keep up with all these new stuff. It is becoming really hard to decide what to learn next or what to focus on.
And as others are saying, know your fundamentals, and know your theory. Get experience doing something real start to finish as often as possible and in order to do that you will have to dive into things. That's how to decide what to learn next.
At the startups that I've worked, things move quickly and unless you have a personal motivation to learn something, you can't keep up.
It's best to get a cursory view of your available options (star them, bookmark them, commit them to memory) and when the situation arises for a specific problem to solve, you'll know of a handful of options to further investigate.
Focus on understanding various modes of thinking, the various key paradigms of programming. Work on understanding basic algorithms, so that given a problem, you can do some rough math and have a general idea of the bounds involved. Spend some effort understanding the low-level stuff.
Long polling's probably been used for over a decade. You should be able to figure out why long polling exists. Think about, for instance, implementing an IRC chat room in the browser, without using any special new features, just HTML and old JS. Once you understand that, you should be able to skim this article, and understand the point and value of the tool without having getting into the details. For me, the point of reading such articles is to see if someone came up with a new way of viewing something, an idea or perspective that might expand how I deal with another problem in the future. Only secondarily do I think I'll use most of the tools I read about (although it's nice to know such a thing exists, for the day you do need it).