How to send long value in UTC format in moment?

Question

Could you please tell me how to send long value in UTC format in moment and AngularJS. Actually I am getting LONG value from server. And then I am showing date in date picker.Now if user select any date from picker. I want to send in same format UTC. Could you please tell me how to send this in UTC

Here is my code
http://plnkr.co/edit/neixp9ZARRAQ33gKSV9u?p=preview

Here is the steps

1. I am getting this from server

   var d = -2208988800000;
   

2. show it on date picker

   var longdate =parseInt(utcMillSecondObj.format('x'));
   

it is working fine.
Now user change the date field using date picker. I want it value in UTC format? Is it possible?

$scope.changedate = function(value) {
  console.log(value)
}

<p class="input-group" ng-if="x.date=='date'">
  <input type="text" 
         view-value-changed='changedate(x.name)' 
         class="form-control" 
         uib-datepicker-popup="{{format}}" 
         ng-model="x.name" 
         is-open="x.opened" 
         datepicker-options="dateOptions" 
         ng-required="true" 
         close-text="Close" 
         alt-input-formats="formats" />
  <span class="input-group-btn">
    <button type="button" 
            class="btn btn-default" 
            ng-click="open1(x)">
      <i class="glyphicon glyphicon-calendar"></i>
    </button>
  </span>
</p>