Messing with js based "classes" & prototypal inheritance in AngularJS

travelLeg.factory.js

(function () 
{
    "use strict";

    angular
        .module('request.travelLegs')
        .factory('TravelLeg', function () 
        {
            let TravelLeg = function (data) 
            {
                let self = this;
                //check the data param to check for a JSON object
                let isDataObject = (typeof data === "object") && (data !== null);

                this.departingFrom = "";
                this.arrivingTo = "";
                this.preferredAirline = "";
                this.isCommercialFlight = true;
                this.mustReturnBy = new Date() + 1;

                if (data && isDataObject) 
                {
                    self.departingFrom = data['departingFrom'];
                    self.arrivingTo = data['arrivingTo'];
                    self.preferredAirline = data['preferredAirline'];
                    self.isCommercialFlight = data['isCommercialFlight'];
                    self.mustReturnBy = moment(data['mustReturnBy']).toDate();
                }
            }

            //returning TravelLeg() constructor to be consumed
            return TravelLeg;
        })

        .factory('FlightLeg', function (TravelLeg) 
        {
            let FlightLeg = function (data) 
            {
                let self = this;
                
                this.departureDate = new Date();
                this.departureTime = moment().format('LT');
                this.rental = {};
                this.hotel = {
                    preferredHotel: ""
                    , checkInDate: new Date()
                    , checkOutDate: new Date() + 2
                };

                if (data) 
                {
                    self.departureDate = data['departureDate'];
                    self.departureTime = data['departureTime'];

                    self.rental = data['rental'];            
                    self.hotel = data['hotel'];
                }
            }
            
            //inherit from TravelLeg superclass
            FlightLeg.prototype = new TravelLeg();

            //returning FlightLeg() constructor to be consumed
            return FlightLeg;
        })

        .factory('ReturnFlight', function (TravelLeg) 
        {
            let ReturnFlight = function (data) 
            {
                let self = this;
                
                this.returnDate = new Date();
                this.returnTime = moment().format('LT');

                if (data) 
                {
                    self.returnDate = data['returnDate'];
                    self.returnTime = data['returnTime'];
                }
            }
            
            //inherit from TravelLeg superclass
            ReturnFlight.prototype = new TravelLeg();

            //returning ReturnFlight() constructor to be consumed
            return ReturnFlight;
        })
})();