HTML5 platform support has been migrated to GitHub as a community-supported Platform Extension and no longer officially supported by Epic in upcoming releases.
HTML5 uses the Emscripten Toolchain from Mozilla to cross-compile C++ into Javascript.
When building content aimed at the HTML5 platform, you can use the guidelines for creating mobile-oriented content as many of the restrictions for mobile development are applicable to HTML5 development.
The following link will allow you to play an HTML5 version of Action RPG right in your web browser.