Adding or appending object with object javascript

i am having 2 objects and the code is

Object 1

var existingValue=self.get('objHubDto').ftd.gridDataDTO.gridDTOMap[name].gridDataMap;

Object 2

var newValue =  self.get('childDataList')

I need to merge/add/append this two in newvalue value eventhough it having duplicate key values