Possible for JavaScript to access XPCOM functions with "out" parameters?

[Chuck Messenger]

I'd like to make an XPCOM interface function with some "out" parameters. 
  For example, I'd like to have:

      boolean Open(in string path, out string errStr);

Is it possible for me to call such a function from JavaScript?  If so, 
how is errStr handled?  For example, the following obviously is wrong:

     var errStr;

     if (obj.Open("file.foo", errStr))
         alert(errStr);

Is it possible to have "out" parameters with JavaScript?  I could always 
redesign my interface in order to not have any "out" parameters, for 
example:

     if (obj.Open("file.foo"))
         alert(obj.ErrStr);

Thanks.


     - Chuck