scope variable updated automatically when I am updating another scope variable

I am getting ajax request data and assigning to one scope variable $scope.customerEvents = data; then I am using another variable to modify the data

    var datanew=data;
    datanew.unshift({'customer_events_id':   'ID','date':'Date','event':'Event','eventsubtype':'Event Subtype','eventtype':'Event Type','time':'Time','user_id':'User ID','user_m':'User MRN','user_name':'User Name','user_role':'User Role'});
    $scope.downloadcsv=datanew;

But customerEvents is getting updated.