req-params-example.js

router.route('/api/categories/:categoryID')
	.get(function(req, res) {
		// query
		connection.query('SELECT listers.lister_id, listers.listing_name, listers.city, listing_categories.category_name FROM listing_categories INNER JOIN listings ON listing_categories.listing_category_id = listings.listing_category_id JOIN listers ON listings.lister_id = listers.lister_id WHERE listings.listing_category_id = ' + req.param('categoryID'), function(err, rows, fields) {
			if(err) {
				res.send(err);
				console.log(err);
				connection.end();
			} else {
				res.send(rows);
			}
		});
	});