Calculate active time of an employee - node.js

Question

I am trying to create a timesheet for employees where I am saving each event(Active, Inactive) as a timestamp in MongoDB. How to calculate the active time of an employee from a given time?
{
"_id" : ObjectId("5d8c8dcca4c6010e29140e0e"),
"activityAt" : ISODate("2019-09-26T10:07:05.388+0000"),
"version" : NumberInt(1),
"deleted_at" : null,
"event" : "ACTIVE",
"employeeId" : ObjectId("5d78fba602c9265fc7ad6273"),
"created_at" : ISODate("2019-09-26T10:07:08.479+0000"),
"modified_at" : ISODate("2019-09-26T10:07:08.479+0000")
}
// ----------------------------------------------
{
"_id" : ObjectId("5d8c8dcca4c6010e29140e0f"),
"activityAt" : ISODate("2019-09-26T11:07:05.388+0000"),
"version" : NumberInt(1),
"deleted_at" : null,
"event" : "INACTIVE",
"employeeId" : ObjectId("5d78fba602c9265fc7ad6273"),
"created_at" : ISODate("2019-09-26T11:07:08.481+0000"),
"modified_at" : ISODate("2019-09-26T11:07:08.481+0000")
}

Answer 1

For every entry that is 'active', take the date from ISODate and subtract from it the current date (or any given time). The result will be all the active time the employee has.
In pseudocode:
active_time = 0
for entry in db:
if entry.event == 'ACTIVE':
active_time = active_time + (current_date - entry.ISODate)
return active_time
The only thing you would need to do is convert the date into something that can be subtracted/added/etc. A solution would be to convert it to hours.
Good luck!