[{"_id":{"$oid":"5ab8d6faff24ae1204000862"},"allotment_details":[{"allotment_id":"468986c5-2155-01e9-74cb-3ad05c66800d","hostel_id":{"$oid":"5ae69fb4d2ccda0e70005551"},"room_id":"ca62d5b5-8fac-62c4-9e62-7e7b9ce9a714","food_preference":"Vegetarian","from_date":{"$date":{"$numberLong":"1527372000000"}},"to_date":{"$date":{"$numberLong":"1528063200000"}},"approved_by":{"$oid":"5af2bda9bc1e370f9c0036d9"},"date_of_allotment":{"$date":{"$numberLong":"1529487464000"}}},{"allotment_id":"c17043a4-7b5b-a132-8226-a4594b61658d","hostel_id":{"$oid":"5ae69fb4d2ccda0e70005551"},"room_id":"ca62d5b5-8fac-62c4-9e62-7e7b9ce9a714","food_preference":"Vegetarian","from_date":{"$date":{"$numberLong":"1527372000000"}},"to_date":{"$date":{"$numberLong":"1530223200000"}},"approved_by":{"$oid":"5af2bda9bc1e370f9c0036d9"},"date_of_allotment":{"$date":{"$numberLong":"1529571140000"}}}]}]

var allotmentDetailsArray = data[0]['allotment_details'];
                      if (typeof allotmentDetailsArray != 'undefined')
                      {
                            if(allotmentDetailsArray.length == 0)
                            {
                              isStudentValidForAllotment =true;
                            }
                            else
                            {
                              //traverse
                             var to_date_of_last_sub_array= data[0]["allotment_details"][lastIndex]["to_date"];

                            }
                      }