Smart comments - update on save

Perhaps this already exists, but I would love my comments to be updated each time I save a file. For example, I have a comment at the start of all my JavaScript files and when I save the file I would like my comment to update, automatically. The comment includes information such as 'Modified By', 'Date last edited', and the file name. A plugin or feature to add a default comment with this information, in my set format, would be really useful; I imagine it would work in the same way as default email signatures - but with variables.