GPL and text

IANAL but my guess is it would depend. Suppose the Javascript just causes a snowflake to appear and drift down any arbitrary web page in which it is included. In this case the page with Javascript seems to be "mere aggregation"

OTOH suppose the Javascript is thoroughly wound into the structure of the page, constantly mentioning specific HTML elements by their ID from deep inside functions, making assumptions about the exact text inside a node and so on. In this case it seems as though the Javascript + HTML are a single work, and arguing that the JS is licensed as a separate work would be laughable.

But then in the latter case the author of the Javascript is probably the owner of the whole work, and nothing prevents creators from asserting license terms that are impossible to fulfil or even totally incoherent. In this case you should treat it as though you weren't offered a license at all.