This has been around for a couple years, but I recently noticed the original disappeared from GitHub, and the developer hasn't been around for a while in his regular hangouts, so I recovered it via the Internet Archive and threw it up on my own server for safekeeping (and simply access!).
rex_sprite (http://www.gridsagegames.com/blogs/fileDownload.php?fileName=rex_sprite.js), by chiguireitor, is "a Node.js module for loading and drawing REXPaint sprites."