:slug or :id ORRRRRR :slugOrId

gistfile1.js

exports.fetchRetailer = function(req, res, next) {
    const queryParams = {};

    if (req.params.id) {
        if (!validator.isMongoId(req.params.id.toString())) {

            logger.error('`retailer.fetchBrand`: invalid retailer param, not a mongo id.', logger.context({
                params: req.params
            }));
            return next({
                code: 404,
                status: 'No retailer found'
            });

        }

        queryParams._id: req.params.id;

    } else if (req.params.slug) {
        queryParams.slug: decodeURIComponent(req.params.slug.trim().toLowerCase());
    } else {
        logger.error('`retailer.fetchBrand`: No retailer id or slug provided', logger.context({
            params: req.params
        }));
        return next({
            code: 400,
            status: 'No retailer id or slug provided'
        });
    }
    
    Retailer.findOne(queryParams, function(err, retailerModel) {