There's a free chapter, chapter 2, so you can see what I mean with the console and what to expect in terms of code examples and approach. So far the feedback I got is that this is a really great way to learn. Plus, the console has an auto-complete feature, so it's a good cheatsheet too.
As the book progresses, the concepts get a little more complicated, so the examples become a little longer, but never too long to type (and Firebug console has a multi-line mode too)
OO concepts - There is a bit of OO theory in chapter 1, it's more of an introduction to the concepts and the OO vocabulary and again, I tried to use examples to make it more clear. Got nice feedback about the presentation of the OO concepts too