how to Calculate sum of multiple durations moment-js?

Question

I am tryng to calculate w total working hours of each user what I did is getting the duration of each day, now I want to calculate the total working hours Given this input durations:[ '0:30:00', '0:30:00', '0:30:00', '1:00:00' ] being respectively half an hour each and the last element being one hour ,

now I want to be able to sum all of these duration to get the total working hours Here's what I managed to do to get the duration I am open to all of your suggestions to improve my already existing code and get my wanted result which is totalHours=HH:mm:ss

 let startTime = moment(book.startTime, 'hh:mm:ss');
      let endTime = moment(book.endTime, 'hh:mm:ss');

      let totalSec = endTime.diff(startTime, 'seconds');
      var durations = moment()
        .startOf('day')
        .seconds(totalSec)
        .format('H:mm:ss');
      result.push(durations);

Answer 1

1. Convert each duration to miliseconds
2. Get the sum of those miliseconds
3. Create moment object to format to hms

const durations = [ '0:30:00', '0:30:00', '0:30:00', '1:00:00' ];

const ms  = durations.map(d => moment.duration(d).asSeconds() * 1000); 
const sum = ms.reduce((prev, cur) => prev + cur, 0);

const hms = moment.utc(sum).format("HH:mm:ss");

console.log('HMS: ' + hms);

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.29.1/moment.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment-timezone/0.5.32/moment-timezone-with-data.min.js"></script>

HMS: 02:30:00