The sources (https://github.com/marijnh/Eloquent-JavaScript) are written in ASCIIdoc which has an epub export. So it should be easy to build one yourself.

There will be one. I haven't gotten around to all the fiddly parts involved in producing a good-looking ebook yet.

CLick on the link to purchase, you can buy a mobi or epub version, or a bundle with the printed book (not ready yet)