Find the mid time value between two time values using momentjs

The middle between two dates is just half of the difference between the dates added to the smaller one.

The difference should be pretty straight forward:

Math.abs(moment(a).diff(b))

Math.abs() removes the minus from negative numbers (aka if a < b).

Calculating the middle has two steps too, first divide the difference by two, then add it to the smaller date (Math.min()):

diff/2+Math.min(moment(a).valueOf(),moment(b).valueOf())

moment(n).valueOf() turns your Date strings into comparable integers.

function middleDate(a,b) {
  let diff = Math.abs(moment(a).diff(b))
  let middle = diff/2+Math.min(moment(a).valueOf(),moment(b).valueOf())
  return moment(middle)
}

console.log(middleDate("2022-01-27T10:30:00Z", "2022-01-27T11:30:00Z"))

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.29.1/moment.min.js"></script>

If you only want the hours and minutes, you can just format the returned moment object (and use moment.utc() to remove the timezone):

function middleDate(a,b) {
  let diff = Math.abs(moment(a).diff(b))
  let middle = diff/2+Math.min(moment(a).valueOf(),moment(b).valueOf())
  return moment(middle)
}

console.log(
  moment.utc(middleDate("2022-01-27T10:30:00Z", "2022-01-27T11:30:00Z")).format("hh:mm")
) 

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.29.1/moment.min.js"></script>

Here is how i solved it

(For my particular case that deals with time only. For more generic cases, you can use the answer above)

import moment from 'moment';
export const middleDate = (startTime, endTime) => {
  let duration = moment.duration(moment(endTime, 'HH:mm:ss').diff(moment(startTime, 'HH:mm:ss'))); //get Total Interval
  let midInterval = duration.asHours() / 2; // find half of the interval
  return moment(moment(startTime, 'HH:mm:ss')).add(midInterval, 'hour').format('HH:mm'); //add the mid interval to the startTime we have
};