IMO, learn pure js but while learning the basics, get your hands dirty with some frameworks, small side projects or tutorials and workshops. This will help you find what framework you enjoy or really "clicks" with your personal preferences. Its also more fun then learning the syntax and structure of a new language. There will be another framework to learn next month but pure js is going to be around for a while.
Some good resources for learning JS from the ground up (pure js)..
Books (highly recommended):
- Javascript: The Definitive Guide
- Eloquent Javascript
- Professional JavaScript for Web Developers 3rd Ed.