extname(url) {
		const name = this.basename(url);
		if (name) return path.extname(name);
		else return null;
	}
@param {String} url
returns the extension of the path, from the last occurrence of the . (period)
character to end of string in the last portion of the path.
If there is no . in the last portion of the path, or if there are no .
characters other than the first character of the basename of path (see path.basename()),
an empty string is returned.
@returns {String}