title_body: Which major eBook reading applications support JavaScript?
upvoted_answer: I don't believe any reader 'fully' supports EPUB3, in part because the EPUB3 and its satellite specs (e.g. annotation, distributable objects, widgets) are so broad that it's not viable for any one reader to implement it all.
  
  On Windows, your best options may be Adobe Digital Editions and Calibre. More detail below.
  
  The Readium project is an open attempt to provide a framework for reader developers with the widest possible support. The Readium Chrome app is a Readium EPUB3 reader, but now that Google has deprecated Chrome Apps it is no longer maintained.
  
  There are readers that support a large proportion of Javascript, though not everything. And this support is poorly documented and hard to debug:
  
  
  iBooks supports Javascript on "iBooks 1.5 or later and iOS 5.0 or later; macOS X Mavericks 10.9 or later". This internal Apple document has details on JS support. It's also possible to enable dev tools (aka Web Inspector) in iBooks.
  The R2 Reader, which is essentially Readium, is available for iOS and Android. Readium uses the operating system's default browser engine, and as such supports a lot of Javascript.
  Adobe Digital Editions uses a derivative of Readium SDK for its rendering engine. So it supports Javascript in a similar way. ADE is flawed in many ways (I find its CSS support very patchy).
  Calibre is an open-source ereader and ebook-management app for Windows, Mac and Linux. It has a complex interface, because it can do so much, so it's not for everyone. It seems to support Javascript and CSS well.
  The AZARDI reader from Infogrid Pacific supports Javascript. I find its UI confusing and its CSS support patchy, too.
  Microsoft's Edge browser once opened epubs and, in theory, supported Javascript. However, Edge's EPUB reader's built-in Javascript heavily restructured the DOM of an epub document, which often breaks any Javascript in the epub itself. Microsoft removed epub support from Edge in October 2019. It's unlikely that epub support will return in future when Edge switches its rendering engine to Chromium.
  
  
  At the moment, Google Play Books documentation says it does not support any Javascript:
  
  
    Google Play Books doesn't support non-standard audio or video tags, or interactive functionality such as that enabled by JavaScript code.
  
  
  FYI, this Ebooks question from a few years ago is similar.
  
  UPDATE Jiminy Panoz maintains the excellent Blitz framework, and he says the following ereaders support Javascript. I've not tested these myself.
  
  
    
    Kobo on iOS and Android
    Readium-based apps in general e.g. CloudShelf Reader, Bookari, Helicon, Lis-a, LEA reader, Infinity Reader.
    Lektz, Gitden on Android/iOS
    Reasily on Android
    Vitalsource Bookshelf on desktop
    Bookworm on Linux
    
  
  
  For more information on various aspects of reader support, see his support data here.