React redux saga - getting some odd behaviour

Question

I am in process of learning how to use reactjs, redux, react-redux and redux-saga. My attempt at this in my public github repo, found here:

https://github.com/latheesan-k/react-redux-saga/tree/5cede54a4154740406c132c94684aae1d07538b0

My store.js:

import { compose, createStore, applyMiddleware } from "redux";
import createSagaMiddleware from "redux-saga";

import reducer from "./reducers";
import mySaga from "./sagas";

const sagaMiddleware = createSagaMiddleware();

const composeEnhancers =
  typeof window === "object" && window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__
    ? window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__({
        // TODO: Specify extension’s options like name, actionsBlacklist, actionsCreators, serialize...
      })
    : compose;

const storeEnhancer = composeEnhancers(applyMiddleware(sagaMiddleware));

export default createStore(reducer, storeEnhancer);

sagaMiddleware.run(mySaga);

my actions.js

export const HELLO_WORLD_REQUEST = "HELLO_WORLD_REQUEST";
export const HELLO_WORLD_RESPONSE = "HELLO_WORLD_RESPONSE";
export const HELLO_WORLD_ERROR = "HELLO_WORLD_ERROR";

export const helloWorldRequest = () => ({ type: HELLO_WORLD_REQUEST });
export const helloWorldResponse = text => ({ type: HELLO_WORLD_RESPONSE, text });
export const helloWorldError = error => ({ type: HELLO_WORLD_ERROR, error });

and my sagas.js

import { put, takeLatest } from "redux-saga/effects";

import { HELLO_WORLD_REQUEST, helloWorldResponse, helloWorldError } from "./actions";

function* runHelloWorldRequest(action) {
  try {
    // TODO: real api call here
    yield put(helloWorldResponse("Hello from react-redux-saga :)"));
  } catch (e) {
    yield put(helloWorldError(e));
  }
}

export default function* mySaga() {
  yield takeLatest(HELLO_WORLD_REQUEST, runHelloWorldRequest);
}

and my helloWorldReducer.js

import { HELLO_WORLD_RESPONSE } from "../actions";

export default (state = "", { type, text }) => {
  switch (type) {
    case HELLO_WORLD_RESPONSE:
      return text;

    default:
      return state;
  }
};

and this is how put it all together on my App component:

class App extends Component {
  componentDidMount() {
    this.props.helloWorldRequest();
  }

  render() {
    return (
      <div className="App">
        <header className="App-header">
          <img src={logo} className="App-logo" alt="logo" />
          <p>{this.props.responseText}</p>
        </header>
      </div>
    );
  }
}

const mapStateToProps = state => ({ responseText: state.helloWorldReducer });
const mapDispatchToProps = dispatch => bindActionCreators({ helloWorldRequest }, dispatch);

export default connect(
  mapStateToProps,
  mapDispatchToProps
)(App);

This works fine, but here's the odd behaviour I am trying to understand. In order to get the response value out of the state and map it into props, I had to do this:

const mapStateToProps = state => ({ responseText: state.helloWorldReducer });

Based on what I saw in the react devtools:

Notice after the request is processed and a response is generated; the resulting state object contains a field called helloWorldReducer.

Where did this come from?

I assumed this field name should have been called text.

P.S. Sorry about the long post; still learning react-redux-saga, so I didn't know which part of my code was relevant to the question at hand.

You Nguyen You Nguyen · Accepted Answer · 2018-10-07T17:25:30

the resulting state object contains a field called helloWorldReducer.

Where did this come from?

It comes from your root reducer which is actually the reducer created by using the combineReducers() method.

This is your reducers/index.js file which export the root reducer for creating redux store:

import { combineReducers } from "redux";

import helloWorldReducer from "./helloWorldReducer";

export default combineReducers({
  helloWorldReducer   // here
});

React redux saga - getting some odd behaviour

1 Answers