Sort Array Object with Multiple Keys[Date and String] [Javascript ,Nodejs]

sortarray.js

var moment = require('moment');
var result = [{
    "rank": 1,
    "u_total_price": 10,
    "user": {
        "_id": "59381ca1d48d69e140518ea3",
        "u_firstname": "Abin",
        "u_created_at": "2017-06-07T15:32:49.240Z"
    }
}, {
    "rank": 2,
    "u_total_price": 9,
    "user": {
        "_id": "5938115e2a1b93e05a274344",
        "u_firstname": "Muhsin",
        "u_created_at": "2017-06-07T16:44:46.745Z"
    }
}, {
    "rank": 2,
    "u_total_price": 9,
    "user": {
        "_id": "59381cafd48d69e140518ea9",
        "u_firstname": "Shajeer",
        "u_created_at": "2017-06-07T15:33:03.943Z"
    }
}, {
    "rank": 2,
    "u_total_price": 9,
    "user": {
        "_id": "59381cdad48d69e140518eb5",
        "u_firstname": "Safeer",
        "u_created_at": "2017-06-07T12:33:46.332Z"
    }
}, {
    "rank": 3,
    "u_total_price": 4,
    "user": {
        "_id": "59381cccd48d69e140518eaf",
        "u_firstname": "Favas",
        "u_created_at": "2017-06-07T15:33:32.488Z"
    }
}]
var sorted = result.sort(function(a, b) {
    var idDiff = b.u_total_price - a.u_total_price;
    if (idDiff) {
        return idDiff;
    }
    var aDate = moment(a.user.u_created_at);
    var bDate = moment(b.user.u_created_at);
    return aDate.diff(bDate, "seconds");
});

sorted.forEach(function(element) {
    console.log(JSON.stringify(element));
});