Converting Text To Js-asp Code

I have a site which uses javascript in an asp document to draw the content
for part of the site from an external .js file.

I want to be able to have a web interface where i can input text, and
convert then save the file to the *.js format. This would involve adding
"document.writeln(' "to the start of each line, and " ');" to the end. This
would also involve adding <!-- to the start of the whole thing, and //--> to
the end.

Would this be possible, and if so how would I go about doing it, are there
any scripts out there that I have missed, or is there a simple way to do it
manually?