Mongoose query - use limit, sort, fields, paging options

query-options.js

const getStories = (category, fields, sort, limit, page, callback) => {
  //default values for these should be moved to config module
  const f = (fields && fields !== 'all') ? fields.replace(new RegExp(',', 'g'), ' ') : (fields !== 'all') ? 'id category headline teaser author create_date' : null;
  const s = (sort) ? sort.replace(new RegExp(',', 'g'), ' ') : '-create_date';
  const l = (limit) ? Number(limit) : 10;
  const p = (page) ? Number(page) : 0;

  //Story here is a previously create Mongoose model
  let query = Story.find({ category: category });

  //Set options
  if (f) query.select(f);
  if (s) query.sort(s);
  query.limit(l);
  query.skip(l * p);

  //Execute
  query.exec((err, stories) => {
    if (err) return callback(err);
    callback(null, stories);
  });
};