Conquer Level 1 First...The Princess can wait!
I would just do what is necessary first. Don't bother with the advanced stuff unless it's absolutely necessary. Most of the things you'll use JavaScript for are very top-level and superficial. Get the syntax, loops, types, etc all down first. Don't confuse yourself with the more difficult aspects of it until you've conquered level 1.
Then Move on to Common Solutions to Common Problems
I would even suggest learning something like jQuery before trying to learn how to extend prototypes, etc. Make yourself useful immediately by learning the stuff you'll be using frequently, and tackle the difficult stuff at a later date when you've got the time.
