State logic in Redux

const ADD = "ADD"

// Reducer to handle states
const messageReducer = (state = [], action) => {
  switch(action.type) {
    case ADD:
      return [...state, action.message]

    default:
      return state
  }
}

// Action creator which creates the action to add a message
const addMessage = (msg) => {
  return {
    type: ADD,
    message: msg
  }
}

// Create the redux store
const store = Redux.createStore(messageReducer)