This book is very effective at teaching Phoenix, the de facto official web framework for the Elixir programming language.
I spend a few hours each day over the course of four days, and quickly breezed through it. Though still in beta, it's easy to follow, and gets straight to teaching your how to build a super cool web app without too much ceremony. It probably helped that I already know Erlang and OTP, and also a bit of Elixir, so I didn't have to spend much time understanding how Phoenix uses OTP, or how language features work. I only experienced a single error in the book where I had to do a bit of bug hunting to figure out that a neccessary step had not been explained in the book which led to a none functioning app. However, when I went to report it to the creators, I saw that the particular bug had already been reported by someone else.
I can highly recommend this book to anyone who wants to make websites and web apps that run on the BEAM virtual machine.