code: function hasMatchingExtname(pathname, exts) {
    var suffix = path.extname(pathname).slice(1);
    return exts.some(function(element) {
      return suffix === element;
    });
  }
docs: Determines if pathname has a matching file extension.
  
  @private
  @param {string} pathname - Pathname to check for match.
  @param {string[]} exts - List of file extensions (sans period).
  @return {boolean} whether file extension matches.
  @example
  hasMatchingExtname('foo.html', ['js', 'css']); // => false