When I was first learning it (4 years ago), I ran into a lot of trouble.
Python has Python.org and documentation in reams. C++ has cplusplus.com, C# has MSDN, PHP has php.net, and so on.
In comparison, W3 schools seems very poorly laid out and not very structured.
I've always liked:
http://eloquentjavascript.net/
and
Big PDF. It's a bit dense, but unambiguous. Nota most bene, though: not every browser implements everything you'll read in the standard. But, if a higher percentage of JS coders would read and grasp the standard, we'd have less confusion about how to use the langauge, IMO.
Don't trust W3 Schools. Despite its name, it is in no way affiliated with the W3C. Take a look at http://w3fools.com