saga.js

import NetInfo from 'react-native';
import { call, put, select, fork, takeEvery } from 'redux-saga';
import * as actions from './actions';
import api from './api';

function* fetchData({ payload }) {
  const isConnected = yield call([NetInfo, NetInfo.isConnected.fetch]);
  if (isConnected) {
    const accessToken = yield select(accessTokenSelector);
    try {
      const { data } = yield call(api.fetchData, accessToken, payload.params);
      yield put(actions.fetchDataSuccess(data));
    } catch (error) {
      yield put(actions.fetchDataError({
        errorType: 'server'
      }));
    }
  } else {
    yield put(actions.fetchDataError({
      errorType: 'offline',
    }));
  }
}

export default function* watchFetchData() {
  yield fork(takeEvery, 'FETCH_DATA_REQUEST', fetchData);
}