While Javascript may not force OOP upon the user, I would say that it can be very much an object oriented language, should you, the programmer, choose to use it as such.
While things like Strings, Dates, Arrays, Windows, etc are all objects which are very much core to using Javascript, these alone would probabaly make it an object-based language, but I would say with all the prototyping facilities available to us - that can be used to easily implement inheritance, etc - make it more of an OOP language.
Have a play with prototyping - you can achieve some remarkable results. I don't remember where I found it, but one of the old Netscape Javascript Guides (I have it as a PDF) really goes into fantastic detail about Javascript and what it is capable of... I still haven't read anything recent that explains it in such detail.
I could be wrong on the OOP thing, but in my experience, most people who say they are Javascript coders have no idea of the true potential of Javascript. Don't take that personally, as I'm not having a dig at you, just saying it how I've expereienced it ;o)
Dan