Redux, a predictable state container for JavaScript apps, is widely used in React applications for managing application state. Redux Thunk and Redux Saga are middleware libraries commonly employed with Redux for managing side effects such as asynchronous API calls, complex state transitions, and more. Both offer solutions for handling asynchronous actions, but they have different approaches and use cases.

Redux Thunk:

Redux Thunk is a middleware for Redux that allows you to write action creators that return a function instead of an action. This function receives the store’s dispatch method, which is then used to dispatch regular synchronous actions or to dispatch further asynchronous actions.

Syntax:

// Action creator using Redux Thunk
const fetchData = () => {
  return (dispatch) => {
    dispatch({ type: 'FETCH_REQUEST' });
    fetch('https://api.example.com/data')
      .then(response => response.json())
      .then(data => dispatch({ type: 'FETCH_SUCCESS', payload: data }))
      .catch(error => dispatch({ type: 'FETCH_FAILURE', payload: error }));
  };
};

Features:

• Simple setup and integration with existing Redux applications.
• Well-suited for simpler use cases and smaller applications.
• Easier to understand for developers familiar with Redux.

Example:

// Reducer
const initialState = { data: [], loading: false, error: null };

const reducer = (state = initialState, action) => {
    switch (action.type) {
        case 'FETCH_REQUEST':
            return {
                ...state,
                loading: true
            };
        case 'FETCH_SUCCESS':
            return {
                ...state,
                loading: false,
                data: action.payload
            };
        case 'FETCH_FAILURE':
            return {
                ...state,
                loading: false,
                error: action.payload
            };
        default:
            return state;
    }
};

// Redux store setup
const store = createStore(reducer, applyMiddleware(thunkMiddleware));

// Dispatching action
store.dispatch(fetchData());

Redux Saga:

Redux Saga is a middleware library for Redux that aims to make side effects in Redux applications easier to manage, more efficient to execute, and simpler to test. It uses ES6 generators to make asynchronous flow control more readable and easier to debug.

Syntax:

// Saga using Redux Saga
import { call, put, takeEvery } from 'redux-saga/effects';
import { fetchDataSuccess, fetchDataFailure } from './actions';
import { fetchDataApi } from './api';

function* fetchDataSaga(action) {
  try {
    const data = yield call(fetchDataApi, action.payload);
    yield put(fetchDataSuccess(data));
  } catch (error) {
    yield put(fetchDataFailure(error));
  }
}

function* rootSaga() {
  yield takeEvery('FETCH_REQUEST', fetchDataSaga);
}

export default rootSaga;

Features:

• More powerful and flexible for complex asynchronous flows.
• Built-in support for cancellation, which can be useful for handling user interactions like cancellation of ongoing requests.
• Allows for easier testing due to the use of generator functions.

Example:

// Redux store setup with Redux Saga
import createSagaMiddleware from 'redux-saga';
import rootReducer from './reducers';
import rootSaga from './sagas';

const sagaMiddleware = createSagaMiddleware();

const store = createStore(rootReducer, applyMiddleware(sagaMiddleware));

sagaMiddleware.run(rootSaga);

// Dispatching action
store.dispatch({
    type: 'FETCH_REQUEST',
    payload: { /* payload data */ }
});

Differences between Redux Thunk and Redux Saga middleware libraries: