The book has 11 chapters totaling 515 pages , several sample apps totaling over 1000+ lines of code (JavaScript/JSX, non-comment lines).

Do I have to know JavaScript?

Yes, we assume you know the basics of the language. But you don't need to be completely up-to-date: we teach the latest language features in case you're not familiar with them.

However, this book teaches React Native from the ground up and you can use it even if you've never written a mobile app before.