Need help in a Redux Challenge

JavaScript
1

I need help to understand the following code.

  1. Why we are creating handleAsync() function?
  2. If we are creating this function, why it’s not being used anywhere?
  3. What does it mean by ReduxThunk.default?
    Your code so far 

const REQUESTING_DATA = 'REQUESTING_DATA'
const RECEIVED_DATA = 'RECEIVED_DATA'

const requestingData = () => { return {type: REQUESTING_DATA} }
const receivedData = (data) => { return {type: RECEIVED_DATA, users: data.users} }

const handleAsync = () => {
  return function(dispatch) {
    // dispatch request action here
    dispatch(requestingData());
    setTimeout(function() {
      let data = {
        users: ['Jeff', 'William', 'Alice']
      }
      // dispatch received data action here
      dispatch(receivedData(data));
    }, 2500);
  }
};

const defaultState = {
  fetching: false,
  users: []
};

const asyncDataReducer = (state = defaultState, action) => {
  switch(action.type) {
    case REQUESTING_DATA:
      return {
        fetching: true,
        users: []
      }
    case RECEIVED_DATA:
      return {
        fetching: false,
        users: action.users
      }
    default:
      return state;
  }
};

const store = Redux.createStore(
  asyncDataReducer,
  Redux.applyMiddleware(ReduxThunk.default)
);

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Link to the challenge: