NPM package sending a generated file to browser

I was trying to use the Excel4Node NPM package to create an .XLS for the user; some formatted output of some mongo collections as an export. The docs (for Node) suggest that you can write to a local file, or send it to the client. The example it uses is a node express route. (I’m using iron router, if that matters)

How do I get it to send the file to the user as an automatic download?

If I don’t give it the second argument, it puts the file in .meteor/local/build/programs/server

I have no idea if I am facing a meteor-space problem or where to begin…