date.js

const Moment = require("moment");
const { extendMoment } = require('moment-range');

const moment = extendMoment(Moment);

var contains = (startDate, endDate, checkDate) => {
    var range = moment.range(startDate, endDate);
    return range.contains(checkDate);
};

module.exports = { contains };

other-file.js

import { contains } from './../some-directory/date.js';

//Objeto sucursal donde se pretende crear la cita
var data = {
    "_id": "5bdb44e14c119d01843ad229",
    "rated": 5,
    "schedule": [
        {
            "startHour": "08:00",
            "endHour": "12:00"
        },
        {
            "startHour": "14:00",
            "endHour": "20:00"
        }
    ],
    "specialSchedule": [
        {
            "startDate": 1542254400000,
            "endDate": 1542686400000,
            "description": "Mantenimiento"
        }
    ],
    "company": "5bdb44e14c119d01843ad228",
    "name": "Av. Lope de Vega",
    "phone": "111-111-1111",
    "address": {
        "street": "Av Lincond",
        "number": 18,
        "township": "Santo Domingo este"
    }
};

willBeOpen = (desiredDate : number) => {
    var isAvailable = data.specialSchedule.filter(date => {
        var desiredDate = 111111111111; //Date timestamp
        return contains(date.startDate, date.endDate, desiredDate);
    });

  //if isAvailable has data means the desiredDate is between a branchoffice's special date 
    return isAvailable.length === 0;
}
var appointmentDate = new Date().getTime();
var isOpen = willBeOpen(appointmentDate);