You could probably implement most of what they do without JavaScript.
But just thinking about my tax return can think of a few features that would have to be dropped, or would become more clunky, like some of the client-side validation, and the auto-saving of drafts.
But just thinking about my tax return can think of a few features that would have to be dropped, or would become more clunky, like some of the client-side validation, and the auto-saving of drafts.