reducer.js

const initialState = {
  /// users is an empty list of a list of users
    users: [],
};

 const userReducers = (state = initialState, action) => {
    switch (action.type) {
        case "ADD_USER":
            return {
              ///the three dots are ES6 syntax(spread operator), it allows you to create copy of an abject
              ///make a copy of `state`
                ...state,
              /// update the copy with the new value
                user: action.payload
            }
        default:
         // otherwise return the existing state unchanged
            return state
    }
}