Calculate the difference between two dates in javascript using react

I'm trying to get the difference between two date in react whith two datepicker and two timepicker ( a react component ). The date is for a booking and I want to get the duration by substract the "end date" with "start date", but when I subtract two date whith more than 24 hours I have a -152 or a value that not corresponding to the real duration.

The code

periodReserve = (e, idPark, title ) => {
let Start_Day = this.state.startDate && this.state.startDate.format(Formatdate);
let Start_Hour = this.state.time && this.state.time.format(formatHour);
let End_Day = this.state.endDate && this.state.endDate.format(Formatdate);
let End_Hour = this.state.timeEnd && this.state.timeEnd.format(formatHour);
let diff = this.state.timeEnd - this.state.startDate;
console.log(diff);}

The code for the first DatePicker and the TimePicker ( for the start )

<DatePicker
  id="calendar"
  className="TestIcon"
  dateFormat='YYYY-MM-DD'
  placeholderText="Date de fin"
  selected={this.state.startDate}
  onChange={this.handleChangeStart}/>

<TimePicker showSecond={false}
     placeholder={time}
     onChange={this.onChangeStart}> </TimePicker>

The code for the second dataPicker and TimePicker

<DatePicker
    id="calendar"
    className="TestIcon"
    dateFormat='YYYY-MM-DD'
    selected={this.state.endDate}
    onChange={this.handleChangeEnd}/>

 <TimePicker showSecond={false}
  placeholder={timeEnd}
  onChange={this.onChangeEnd}> </TimePicker>

Sample code using momentJS

this.state = {startDate:1519026163000, timeEnd:1519126755000} // example

const startDate = moment(this.state.startDate);
const timeEnd = moment(this.state.timeEnd);
const diff = timeEnd.diff(startDate);
const diffDuration = moment.duration(diff);

console.log("Total Duration in millis:", diffDuration.asMilliseconds());
console.log("Days:", diffDuration.days());
console.log("Hours:", diffDuration.hours());
console.log("Minutes:", diffDuration.minutes());
console.log("Seconds:", diffDuration.seconds());

<script src="https://momentjs.com/downloads/moment.js"></script>