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

I have a JSON object like this:

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

  { poster_ip: '127.0.0.1',
    post_body: 'example',
    __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',
    __v: 0,
    newName: NewValue },

  { poster_ip: '127.0.0.1',
    post_body: 'example',
    __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 JSON object is the result i get from a mongodb query.