This would be a 3.5 star is I could rate it that. I think my expectations were off going into this, as I expected an "in depth" look at language features for people who already knew JavaScript. Instead, I felt like it was also trying to teach the language to newcomers and spent a lot of time on bits and pieces that I would assume someone who works with the language would already know.

It moves incredibly quickly, which for the most part is a point in its favor. In several spots, though, I wish the author would have been clearer on why a specific technique is bad beyond "this is bad, don't do it". It's strongest cases are when it's showing side-by-side examples of code illustrating why certain things are better one way or the other. On the flip side, the whole first section is dedicated to diagramming out the grammar of the language. The amount of space dedicated to this as opposed to the "awful parts" later in the book seems imbalanced to me.

In the end, I learned some new stuff about the language, but I had already seen a good portion of the content in other places. I'd recommend this whole-heartedly to someone with a strong technical background that isn't already familiar with JavaScript. For folks who already have a decent understanding of modern JavaScript, read the section on functions and inheritence and skim the rest.