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That book was written in 2008. JavaScript classes were introduced with ECMASCRIPT 2015.

JavaScript classes are syntactic sugar, the class type doesn't exist in ES2015; everything still works with prototypical inheritance.

So, I'd say that this book is still relevant Today. If you don't understand how inheritance work behind the scenes, you don't understand JavaScript.

That doesn't really matter, this complaint about "this" predates the use of classes.