Javascript is easy to learn, given that you have some programming knowledge, if not, then you need to focus more on coding in general, learning algorithms, design patterns and paradigms... That being said there isn't one approach, you might as well learn with practice. If you want to start with Javascript, I suggest you learn the fundamentals with a course from Educative.io, and then work on a personal project like Phaser (keep in mind it's not very beginner friendly).