How to add to an array within existing json object in Angular?

My json object, "flowComponents" contains a string (name) and an array of strings (edition). For example:

    {
  "_id": "553e87f3205465e83b46999b",
  "name": "FLOWCOMPONENT_CONTACTCOMBINATION_EDITION",
  "__v": 0,
  "edition": [
    "billing",
    "billingDelivery",
    "default",
    "deliveryAddressOnly",
    "deliveryBillingLicensee",
    "deliveryBillingLicenseeWithWrapper",
    "deliveryLicensee",
    "deliveryOnlyCopyToAll",
    "licenseeDelivery",
    "sassDefault",
    "sassDeliveryOnlyCopyToAll"
  ]
}

I need to add/concat another edition to this existing flowComponents object. My form has a dropdown with the names of the existing flowComponents, and a text area that makes an array of each line of text:

<form ng-submit="addToExistingFlowComponent()">
    <div class="interact">
        <select ng-model="existingName" chosen options="flowComponents" ng-options="item as item.name for item in flowComponents" data-placeholder="Select a flow component...">
            </select>
    </div>

    <div class="interact">
        <label class="interact-label">Enter each edition on a new line.</label>
        <textarea id="text_area" placeholder="Edition" ng-model="existingEditionList" ng-list="&#10;" ng-trim="false"></textarea>
    </div>
    <button type="submit">Submit</button>
</form>

This is the add edition method in my controller:

$scope.addToExistingFlowComponent = function(){
  if(!$scope.existingName || $scope.existingName === '') { return; }

  var existingFC = $scope.existingName._id;

  sendAppData.postEdition( existingFC, {
    edition: $scope.existingEditionList
  });

  $scope.existingName = '';
  $scope.existingEditionList = '';
}; 

And this is the method that posts the data to the server:

this.postEdition = function(existingFC, newEdition) {
   return $http.post('/new-flow-component', newEdition).success(function(data){
        flowComponents.push(data);
    });
};

The problem is, this is pushing the data to a new object rather than adding to the existing object. I'm able to pass the _id of the existing object to the existingFC parameter, but I can't figure out how to get that inside of function(data) in order to push it into the correct edition array.