Recommend a javascript framework?

Crafty looks like it's a solid choice, so use it if you like it. You could also check out Construct 2 and see if it fits your preferences better. Both of those are definitely way up at the top for HTML5 development.

If you decide you don't like either of those, search for HTML5 game engines instead of javascript frameworks. Even engines like Entity JS show up in HTML5 searches. But Crafty and Construct 2 are pretty much the top contenders, so I wouldn't worry too much about searching for others if one of those two works.

I'm a fan of LimeJS, it has an API modeled on Cocos2D and works well on mobile.

If you don't mind commercial licencing Impact is a nice library.

Crafty is a good option, but the documentation is almost non-existent and it can be hard to get started or figure out some of the more complex details unless you're willing to dig through the source. Note that the getting started guide is provided by a third party.

I've also hard good things about the above-mentioned LimeJS, but don't have any personal experience with it.

Construct 2 (also suggested above) is an excellent development environment if you want to create HTML5 games -- it's more than capable of simple games like you're after, it's extremely well crafted, updated frequently, has excellent documentation, and has an active community -- but it's definitely not what you'd consider a "JavaScript framework" like many of the other options; it's much more akin to Game Maker, and has you create games using a simple editor for snapping together configurable behaviours and a surprisingly capable visual event system, although it does expose a JavaScript plugin SDK.

Hope that helps!

While I haven't tried it, Phaser looks like a nice js/HTML5 game framework