JSZip 
A library for creating, reading and editing .zip files with Javascript, with a lovely and simple API.
See http://stuartk.com/jszip for all the documentation.
var zip = new JSZip();
zip.file("Hello.txt", "Hello World\n");
var img = zip.folder("images");
img.file("smile.gif", imgData, {base64: true});
var content = zip.generate({type:"blob"});
// see FileSaver.js
saveAs(content, "example.zip");
/*
Results in a zip containing
Hello.txt
images/
smile.gif
*/License
JSZip is dual-licensed. You may use it under the MIT license or the GPLv3 license. See LICENSE.markdown.