Stackverflow 29199010

HTML

<script src="https://cdn.firebase.com/js/client/2.2.3/firebase.js"></script>

JavaScript

var notifications = { 
  "001": { 
    "member_id":      "123",
    "created_at":     1424357680681,
    "new":            true,
    "first_name":     "Jon",
    "last_name":      "Snow",
    "message":        "likes your photo"
  },
  "002": { 
    "member_id":      "456",
    "created_at":     1424357680681,
    "new":            true,
    "first_name":     "Clark",
    "last_name":      "Kent",
    "message":        "likes your comment"
  }
};

var ref = new Firebase('https://fir-sample-ce8e1.firebaseio.com/');

//ref.set(notifications);

ref.orderByChild("member_id").equalTo('456').on("child_added", function(data) { 
       console.log("new child id = " + data.key());
    });