Best way to learn Javascript?

What more precisely is your aim? You could 'learn javascript' and still not have a clue (e.g., what's taught in most programming classes). There are lots of 'bad' javascript code snippets out there (in the form of tutorials or otherwise) so I feel a slightly better approach would be to go along the lines of, "hey I want to do <something>" and then go find out how to do it either by finding a convenient tutorial, or getting your head stuck in to reference material. The latter will be much more beneficial to you in the long run.

If you see something on the web and ask yourself how they did it, go find out by digging through their source code. JavaScript is wonderful in that way, we can get our hands on it (though it's not always easy to deciper!).