mhemesath/node-wkhtml — pull request #7 by bencpeters (2012-04-20 05:17:29+00:00)
Title: Changed to use "spawn" instead of "exec"

Also, unified functionality somewhat along the lines that you proposed,
so that everything uses the single function "convert" instead of having
"convert" and "convertAs". Now, if no filename is given to have the
command save locally, the function includes the data in a buffer to the
callback function for the user to do with as they please.

I haven't tested it extensively, but it seemed to work on my example server.
If you want to have the unified interface different than the one I propose here, by all means go ahead.