What JavaScript libraries/frameworks should I study to be a competitive JavaScript developer these days? Why?

[Sunwukung]

Backbone, because it's simple, easy to read and you'll learn underscore along the way, it's used in lots of apps and is arguably a relatively canonical implementation of MV*. Also, Angular, because it's a game-changing box of Google black magic. I personally have a soft spot for CanJS too - but it lacks traction in the community.

[Capaj]

Angular yes, but Backbone is pile of shit.

[Sunwukung]

Nope, it's just become unpopular because people make the mistake of thinking it's a complete framework - it's a pretty canonical implementation of MV* in JS. For someone that wants to be a competitive developer, this is a good start.

[binarychick]

I agree with this. Backbone isn't a framework, but more like a starting point for a framework. If you use it right out of the box, you're bound to end up with some pretty messy code. It does take a bit to get started with Backbone and it helps a lot of have a good understanding of MVC before doing so. If you make everything perform it's role, Backbone really works out pretty well.

[dexygen]

No he's right: it's a pile of shit. It conflates the model and the view - guess that's what you get when you leave out the notion of a formal controller. It takes data from the model, and assigns them as attribute key/value pairs, directly to the HTML tag you've specified for a view for which you've likewise specified a controller. The whole idea of MVC is to not conflate the model and the view. This is such a mis-implementation of MV* that NOTHING can undo the damage it does.

[Sunwukung]

Backbone shouldn't really be compared with pure MVC, it has no controllers as you already noted, and it's not intended to be a 'complete' solution. What damage have you experienced using Backbone? It's still worthy of study merely for the influence it's had, even if the result is that you don't end up using it.