This library is not maintained please consider using markdown-it, marked or some other well maintained package instead.
Origianlly library contained Showdown packaged for node/npm as in early days there was no alternative available. Since it has being discovered to contain three regular expressions vulnerable to catastrophic backtracking. Given a multitude of better options today this package was just updated to wrap markdown-it to avoid breaking existing dependencies, but then again there is no reason to prefer it over other well maintained library.