JavaScript libraries related to different file types.
HTML: http://html2canvas.hertzen.com/ , https://github.com/bgrins/DrawWindow</p>
Java: https://github.com/notmasteryet/jvm-js, https://github.com/nzakas/props2js (.properties files only)
JPEG: https://github.com/notmasteryet/jpgjs , http://www.syntensity.com/static/openjpeg.html</p>
PNG: https://github.com/devongovett/png.js , https://github.com/pkrumins/node-png</p>
SVG: http://code.google.com/p/canvg, http://github.com/kangax/fabric.js</p>
WebP: http://badassjs.com/post/1313384987/weppy , http://webpjs.appspot.com/</p>
In addition you might want to check out filer. It wraps HTML5 Filesystem API. See also this article.