Does this existing anywhere in the world? (javascript download progress meter)

Hello,

I've read quite a bit of discussion on different approaches of how to
create a download progress meter that can be implemented into a Web
site. I understand that by the very nature of the way the download
transport is handled that this cannot "automatically" be done...
upload progress meters exist, but not download. However, I've seen
different theories on how it could be done if one knows the file size.
Is anyone aware of a working download meter script written in
JavaScript?

Sincerely,

Julia