How to open an Excel document using JavaScript code and without using an ActiveX control object like:
var myApp = new ActiveXObject("Excel.Application");
myApp.workbooks.open("test.xls");
It's possible to open .xlsx files with Javascript because they are ZIP packages. This has been experimented with XForms: http://www.w3.org/community/xformsusers/2012/12/19/editing-zip-with-xforms/