Redux questions.

//Question how do I get the responseText back on my loginReducer?
//Code below is working on the example, just some snippets, I think im close to understanding but not completely.

//Actions:
        fetch('https://google.com')
            .then((response) => response.text())
            .then((responseText) => {
                console.log(responseText);
            dispatch(actionsCreators.succesLogin(responseText));

//Const actionsCreators
//how does 'data' or any other type of variable work here? related to reducers or
    succesLogin: (data: Object): Object => ({
        type: actionsTypes.SUCCES_ON_LOGIN,
        data
    }),

//Initial State
//Should data be part of initial state?
const initialState = {
    isLoggedIn: false,
    waitingSymbol: false,
    error: ""
};

//loginReducer:
//how to get the passed back variables here?
const loginReducer = ( state = initialState, action ) => {
    switch (action.type) {
        case types.SUCCES_ON_LOGIN:
            return Object.assign({}, state, {
                isLoggedIn: true,
                waitingSymbol: true,
                error: "Login success"
            });
    }
}