As someone currently using (aka fighting) the web audio API, there's definitely a market for better, clearer information out there, but I'm curious how successful targeting a such a niche market has been?
The book I wrote is a "how to program" book that uses JavaScript coupled with the Web Audio API as a tool to appeal to sound artists. It is not a book to teach those who already know how to program the Web Audio API. When I've gone on Amazon to look at beginner programming books I've found that most "themed" books are directed to those who want to learn how to build websites, mobile apps or games - but none are directed to DJ's, electronic musicians, sound artists etc. I wrote a book that does just that, but as it stands I have no idea if it will sell.