It's a book about Javascript that assumes you've written software in other languages before. I believe the book uses Java/C#, Python, and maybe a couple other languages as reference points.

It describes language behavior and constructs that may be new to you, and details where the familiar may differ from what you'd expect. For instance, the section on `var` and how function scoping (and hoisting) differ from block scoping was quite detailed, but I don't remember it spending a lot of time on what it meant to declare a variable or why scoping rules matter.

If the book had a beginner focus I might have seen the section on declaring variables, skimmed to see the `var` keyword, and skipped the rest. Then I'd have written a bunch of code that would bite me later, because why would you ever assume function scoping when coming from another language?

It's unfortunate that it's so difficult to find books with either an intermediate to advanced focus, or a focus on switching languages, as I think both are sorely needed in the current programming ecosystem.

[0]: https://www.wiley.com/en-us/Professional+JavaScript+for+Web+...

[1]: https://www.amazon.com/Professional-JavaScript-Developers-Ma...