I'm writing a WebAssembly book: Early Access for WebAssembly from the Ground Up
If my memory serves me well, last year I went to Munich to have some beers with Patrick Dubroy and I mentioned that I was planning to write a small book about WebAssembly by writing toy compilers for small weird languages.
He mentioned that he was thinking about something similar and if I wanted to write it together, I said yes and the rest is a blog post announcing the public release of the Early Access of WebAssembly from the Ground Up :)
The ideas evolved over time but we settled on a "digital first" book that would allow us to experiment with interactive elements inspired by the Explorable Explanations movement and similar ideas like Bret Victor's Learnable Programming.
The first 6 chapters are already available and after the launch we are going to go back to "writing mode" to complete the rest.
If you are interested in learning the fundamentals of WebAssembly by building a compiler for a simple programming language step by step using JavaScript and OhmJS this book may be for you.