knockout - dependent object attributes when managing an array

Question

I have a view model which is basically an array of objects. The object has a StartDate and an EndDate attribute. I am trying to implement a functionality wherein the EndDate of the previous item in the array should be T - 1 of the StartDate of the current item. For eg:

If the array is something like:

   Type      Start Date       End Date
   ObjectA   5/1/2014         5/31/2014
   ObjectB   6/1/2014

Now, when the user changes the ObjectB's StartDate to lets say 6/15/2014, ObjectA's EndDate should automatically change to 6/14/2014.

How can I achieve this with knockout? Please help.

Answer 1

ObjectB start date should be observable. Then subscribe to observable property and when it changes, change property of ObjectA.

function addDays(date, value) {
            return new Date(date.getFullYear(), date.getMonth(), date.getDate() + value, date.getHours(), date.getMinutes(), date.getMilliseconds());
        }

ObjectB.StartDate.subscribe(function (newDate){
  ObjectB.EndDate(addDays(newDate, -1));
});