Clean backend routing

/*jslint es6, node: true */

(function () {
    "use strict";

    const express = require('express');
    const router = express.Router();
    const Lesson = require('../models').Lesson;

    const getAllLessons = function () {
        return Lesson.findAll();
    };

    const getLessonById = function (id) {
        return Lesson.findById(id)
            .then(function (lesson) {
                if (!lesson) {
                    throw {code: 404};
                }

                return lesson;
            });
    };

    router.get('/', function (ignore, res) {
        getAllLessons()
            .then(function (lessons) {
                res.json(lessons);
            })
            .catch(function () {
                res.sendStatus(500);
            });
    });

    router.get('/:id', function (req, res) {
        getLessonById(req.params.id)
            .then(function (lesson) {
                res.json(lesson);
            })
            .catch({code: 404}, function () {
                res.sendStatus(404);
            })
            .catch(function () {
                res.sendStatus(500);
            });
    });

    module.exports = {router};
}());