And that's one reason why the majority of ebooks purchased by consumers aren't in epub format.[1]
For the vast majority of fiction a format constrained to bold, italicize, paragraph break, chapter heading, and chapter break allows a far superior user experience.
JavaScript isn't a necessary component of ePub readers. Besides a handful of apps like Adobe Digital Editions and Apple iBooks, most don't. Kobo doesn't in their eReaders. JavaScript is only used in ePubs for multimedia crap. Fiction ePubs don't bother either.
Kindle books generally start their life as ePubs that Amazon then converts to their formats before they list them. They don't even let you publish in mobi anymore.
Kindle's lack of MathML support actually makes the user experience worse for everyone. Publishers often make 1 ePub they submit to multiple stores so rather than make a MathML version and a shitty image version for Kindle they just make a shitty image version and now you have a math textbook that's larger than the PDF would have been AND the equation text isn't resizable defeating the whole point of a reflowable ebook.
> Kindle books generally start their life as ePubs that Amazon then converts to their formats before they list them. They don't even let you publish in mobi anymore.
Morally speaking they start as Kindle ePubs that support a very very limited subset of the ePub standard.
For the vast majority of fiction a format constrained to bold, italicize, paragraph break, chapter heading, and chapter break allows a far superior user experience.
[1] https://magnoliamedianetwork.com/ebook-publishing-platforms/