Using a C++ class inside Javascript without an .idl

Question

It is possible to call methods on a class whose interface is not exposed through an .idl file?

Im my particular case, I'd like to use the @mozilla.org/gfx/fontmetrics;1 class, whose interface nsIFontMetrics doesn't have a correspondent .idl file.

Answer 1

Nope. If there is no idl file, it isn't exposed to script through XPConnect.