I find the old-school Netscape 4 JavaScript docs very useful for this purpose. Although they're obviously totally outdated, and some of the DOM features in them like Layers are long gone, for the language basics they're really solid.
That's because before the days of IE supremacy and ECMA standardisation, Netscape's JavaScript was the definitive JavaScript. Other browsers pretty much had to implement exactly what you see in those old docs.
They're also much easier to read than the ECMA-262 document, which even by the standards of standards documents is an absolute horror.
