api.js

var express = require('express');
var router = express.Router();

router.use('/playlists', require('./playlists'));
router.use('/songs', require('./songs'));

module.exports = router;

index.js

var express = require('express');
var app = express();

app.set('json spaces', 2);

app.use('/api', require('./api'));

app.listen(3000);

playlists.js

var express = require('express');
var router = express.Router();

var playlists = [
  { id: 1, title: 'Rock', songs: [4,5,6,7] },
  { id: 2, title: 'Pop', songs: [1,2,3] },
  { id: 3, title: 'Jazz', songs: [8,9,10,11,12] }
];

router.get('/', function (req, res) {
  res.json(playlists);
});

router.param('id', function (req, res, next, id) {
  var item = playlists.filter(function (item) {
    return item.id == id;
  });
  req.playlistItem = item.length ? item[0] : null;
  next();
});

router.route('/:id')
  .get(function (req, res, next) {
    return req.playlistItem ? res.json(req.playlistItem) : next();
  })
  .post(function (req, res) {
    // create item
  })
  .put(function (req, res) {
    // update item
  })
  .delete(function (req, res) {
    // delete item
  });


// handle "/api/playlists/1/songs/" as well
router.use('/:id/songs', require('./songs'));


module.exports = router;

songs.js

var express = require('express');
var router = express.Router();

var songs = [
  { id: 1, artist: 'Madonna', title: 'Living for Love' },
  { id: 2, artist: 'Madonna', title: 'Ghosttown' },
  { id: 3, artist: 'Madonna', title: 'Like a Prayer' },
  { id: 4, artist: 'Red Hot Chili Peppers', title: 'Californication' },
  { id: 5, artist: 'Red Hot Chili Peppers', title: 'Under the Bridge' },
  { id: 6, artist: 'Bruce Springsteen', title: 'Born in the U.S.A.' },
  { id: 7, artist: 'Bruce Springsteen', title: 'Dancing in the Dark' },
  { id: 8, artist: 'Miles Davis', title: 'Blue in Green' },
  { id: 9, artist: 'Miles Davis', title: 'So What' },
  { id: 10, artist: 'Nina Simone', title: 'Feeling Good' },
  { id: 11, artist: 'Nina Simone', title: 'My Baby Just Cares for Me' },
  { id: 12, artist: 'Nina Simone', title: 'I Put a Spell on You' }
];

function filterByPlaylist(playlist, songs) {
  if (playlist) {
    songs = songs.filter(function (song) {
      return playlist.songs.some(function (songId) {
        return songId == song.id;
      });
    });
  }
  return songs;
}

router.get('/', function (req, res) {
  res.json(filterByPlaylist(req.playlistItem, songs));
});

router.param('id', function (req, res, next, id) {
  var item = filterByPlaylist(req.playlistItem, songs)
    .filter(function (item) {
      return item.id == id;
    });
  req.songItem = item.length ? item[0] : null;
  next();
});

router.route('/:id')
  .get(function (req, res, next) {
    return req.songItem ? res.json(req.songItem) : next();
  })
  .post(function (req, res) {
    // create item
  })
  .put(function (req, res) {
    // update item
  })
  .delete(function (req, res) {
    // delete item
  });


module.exports = router;