How can I get available datetime or datetime range by comparing from user x's schedule and user y's schedule

How can I get available datetime or datetime range by comparing from user x's schedule and user y's schedule.

Result should be as drop-down list of available datetime(s) for both users.

if user x available on 30/11/2019 15:00 and user y is also available on the same time. As result I can schedule them.

Could be done in JavaScript / Lodash.

I can't think of script which would able to do this.

With kind regards, Vic.

via Chebli Mohamed