[jstx1]

Read some, then move on and learn new things as you need them.

Jumping in completely cold can lead to huge wastes of time because you don't know what you're doing. So read that book on a new language, follow the offical tutorial for a new framework, go over the docs etc. But make sure to time box that learning and then move on to doing some real work because otherwise you can get stuck on the learning phase forever.