mongooseで配列を_idで検索する

javascript初心者です。
nodejsの処理でmongodbから値と取り出す処理です。
下記のjsonデータの中でcommentsは配列になっておりますが、
この配列から指定した_idのデータを取り出す処理ですが、
id(req.params.commentId)で取得できるのですが、
なぜかわかりません。mongooseの機能でしょうか？

自己解決しました。
http://mongoosejs.com/docs/api.html#types_documentarray_MongooseDocumentArray.id

javascript
1Dishes.findById(req.params.dishId).populate('comments.postedBy').exec(function(err, dish) {
2    if(err) throw err;
3    res.json(dish.comments.id(req.params.commentId));
4})

json
1{
2  "_id": "58d6382b77fe4c0e9c3623f2",
3  "updatedAt": "2017-03-25T09:59:17.867Z",
4  "createdAt": "2017-03-25T09:28:11.185Z",
5  "name": "Uthapizza",
6  "image": "images/uthapizza.png",
7  "label": "Hot",
8  "price": 499,
9  "description": "A unique combination",
10  "__v": 4,
11  "comments": [
12    {
13      "updatedAt": "2017-03-25T09:28:11.184Z",
14      "createdAt": "2017-03-25T09:28:11.184Z",
15      "rating": 5,
16      "comment": "Imagine all the eatables, living in conFusion!",
17      "_id": "58d6382b77fe4c0e9c3623f3",
18      "postedBy": null
19    },
20    {
21      "updatedAt": "2017-03-25T09:58:04.110Z",
22      "createdAt": "2017-03-25T09:58:04.110Z",
23      "rating": 2,
24      "comment": "qqqqqqqqqqqqqqqq!",
25      "postedBy": {
26        "_id": "58d5e18c77fe4c0e9c3623f1",
27        "username": "fff",
28        "__v": 0,
29        "admin": true,
30        "lastname": "kakiku",
31        "firstname": "aiueo"
32      },
33      "_id": "58d63f2c0713cd3dccfd4458"
34    },
35    {
36      "updatedAt": "2017-03-25T09:59:17.867Z",
37      "createdAt": "2017-03-25T09:59:17.867Z",
38      "rating": 3,
39      "comment": "eeeeeeee!",
40      "postedBy": {
41        "_id": "58d5e15f2835921284b8af0d",
42        "username": "eee",
43        "__v": 0,
44        "admin": false,
45        "lastname": "",
46        "firstname": ""
47      },
48      "_id": "58d63f750713cd3dccfd4459"
49    }
50  ],
51  "category": "mains"
52}