Hmm. I can't say for absolute sure, but if the root document is HTML and there are no <script> tags (or <iframe>s, I guess), I don't see how you'd get JavaScript to execute. I think those are strictly the only entry-points JS can have, and it's not like HTML or CSS could mutate the document to create one after the fact.
EDIT: I brainfarted and totally forgot about inline event handlers. Go easy on the downvotes please.
EDIT: I brainfarted and totally forgot about inline event handlers. Go easy on the downvotes please.