How can I update an array in state? - reactjs

Question

When my app loads I generate some initial data. My initial state is:
const INITIAL_STATE = { calendarData: [ ], index: 0 }
The data generated is an array of objects:
[
{
"date": "2017-09-24T16:13:24.419Z",
"id": 0,
"swiped": false,
"uri": "http://www.someurl.com/24.png",
},
{
"date": "2017-09-25T16:13:24.426Z",
"id": 1,
"swiped": false,
"uri": "http://www.someurl.com/25.png",
},
{
"date": "2017-09-26T16:13:24.426Z",
"id": 2,
"swiped": false,
"uri": "http://www.someurl.com/26.png",
}
]
I'm attempting to update calendarData like so:
return {...state, calendarData: [...state.calendarData, ...aboveArray]};
However, when I log mapStateToProps
const mapStateToProps = state => {
return { calendarData: state.calendarData };
};
Console shows the following:
Object {
"calendarData": Object {
"calendarData": Array [],
"index": 0,
},
I am trying to update the empty calendarData array in INITIAL_STATE with the new array of objects.
Before I made this change I was initializing state = [] and returning the aboveArray, which worked. Now I want my state to be an object that has a calendarData array and an index key,
state = {
calendarData: [],
index: 0,
}