How to add an extra element in every nested array of a MongoDB object?

I have a MongoDB object like this:

[ 
   { poster_ip: '127.0.0.1',
    post_body: 'example',
    _id: 54fc1f7808bac08f6d25f24b,
    __v: 0 },

  { poster_ip: '127.0.0.1',
    post_body: 'example',
    _id: 54fc1f7808bac08f6d25f24a,
    __v: 0 } 
]

how can i add an extra element to every nested array so it would be like this:

[ 
   { poster_ip: '127.0.0.1',
    post_body: 'example',
    _id: 54fc1f7808bac08f6d25f24a,
    __v: 0,
    newName: NewValue },

  { poster_ip: '127.0.0.1',
    post_body: 'example',
    _id: 54fc1f7808bac08f6d25f24b,
    __v: 0,
    newName: NewValue },
]

I tried this but it didn't work:

for(var i=0; i<JSONobject.length; i++){
    JSONobject[i].newName= NewValue;
}

I'm using node.js, the object is the result i get from a mongodb query.

Here is the function:

exports.Posts = function(UserID, PostID, callback) {

                Post.find( { post: PostID } , function(err, results) {

                var r = results.toObject(); //here i get error 'has no method toObject'

                for (var i=0; i<r.length; i++){
                    r[i].newName = "NewValue";
                }

                console.log(r);
                    //i don't see any changes here with console.log

                    return callback(null, results);
                });
}

EDIT:

After a little more research i found out that the returned Mongoose Document isn't a JSON object, so i'm trying now to convert it to an object.