Typically a newbie will ask about which framework they should learn. There will be a bunch of "it depends" and "try them out" responses, and then someone will take pity and pick a clear direction based on their experience.
Well and good.
But this way the newbie can learn from the actual experience of lots of other people. Data, for short.
I can tell here what tech I need to focus on for my pet project, which will also improve my hirability looking forward.
Honestly the easiest way to learn this is to contact your local recruiters and ask them to send you some openings for FED positions.
In nearly every one, you will see which JS framework is the main one they use. In my recent experiences (the last two or three years) most corporate environments are using AngularJS, while the smaller startups are using React and some mix of various other libraries for their apps and sites.
There are still a few agencies I know using BackboneJS, since it was in that first wave of JS frameworks and there's apps and sites out there which still need supporting.
People generally put forward one of the following: Knockout (easy to learn), Ember, Backbone, Angular, React.
Someone will invariably say no, use nothing but plain Javascript at first. This will lead to a little subthread about whether it is fair to include jquery.
Every now and then someone will come up with meteor or vue as an alternative.
Unfortunately the JavaScript ecosystem is frothy enough that a lot of junior developers are inevitably going to waste time learning technologies that will be considered obsolete by the time they have mastered them.
Seeing what people are hiring for is of course a useful signal too but it's easy to become a COBOL programmer if that's the only thing you look at.
When a technology is less popular than it used to be, there's also a glut of experienced talent in that technology. That's why trends matter more than just a point snapshot in choosing what to learn, if you're looking at employability.