Redux-Saga controllable long-polling loop

redux-saga-poll-loop.js

import {  take, put, call, fork, cancel, cancelled } from 'redux-saga/effects'

import {EVENT_POLLING_START, EVENT_POLLING_STOP} from "constants/eventPolls";
import {ClientEventType} from "constants/serverEvents";



function* handleEventA(serverEvent) {
    yield put({type : serverEvent.type, payload : {name : serverEvent.eventAData}});
}

function* handleEventB(serverEvent) {
    yield put({type : serverEvent.type, payload : serverEvent.eventBData});
}

function* handleEventC(serverEvent) {
    const {eventCData} = serverEvent;
    const {field1, field2} = eventCData;
    yield put({type : serverEvent.type, payload : {field1, field2}});
}

function* defaultEventHandler(serverEvent) {
    console.log("Unhandled server event type: ", serverEvent.type);
}

const serverEventHandlers = {
    [ClientEventType.EventA] : handleEventA,
    [ClientEventType.EventB] : handleEventB,
    [ClientEventType.EventC] : handleEventC,
}


function* handleServerEvent(serverEvent) {
    const eventHandler = serverEventHandlers[serverEvent.type] || defaultEventHandler;

    return yield eventHandler(serverEvent);
}


function* pollForEventsLoop(serverRPC) {
    let lastCallSucceeded = true;
    try {
        while(true) {
            const serverEvents = yield call(serverRPC.pollForEvents, lastCallSucceeded);
            yield serverEvents.map(handleServerEvent);
        }
    }
    finally {
        if (yield cancelled()) {
            console.log("Event poll loop cancelled");
        }
        console.log("Event poll loop ended");
    }
}


export default function* pollForEventsDriver(serverAPI) {
    const {serverRPC} = serverAPI;

    while ( yield take(EVENT_POLLING_START) ) {
        // starts the task in the background
        const pollForEventsTask = yield fork(pollForEventsLoop, serverRPC);

        // wait for the user stop action
        yield take(EVENT_POLLING_STOP);
        // user clicked stop. cancel the background task
        // this will throw a SagaCancellationException into the forked bgSync task
        yield cancel(pollForEventsTask);
    }
}