Polling with redux-saga

polling-saga.js

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

function delay(duration) {
    const promise = new Promise(resolve => {
        setTimeout(() => resolve(true), duration)
    });
    return promise;
}

// Fetch data every 20 seconds
function* pollData(url) {
    try {
      yield call(delay, 20000);
      const response = yield call(get, url)
      // TODO: pass condition as argument to pollData instead of calculating it in the function
      const condition = 'use-response-to-calculate-if-condition-is-met'
      // TODO: pass action type information as argument to make polling function more flexible
      if (condition) yield put({type: 'POLL_CONDITION_MET', ...response})
      else yield put({ type: 'POLL_FOR_X', url })
    } catch (error) {
      yield put({ type: 'POLLING_ERROR', error })
      return;
    }
}

// Wait for polling action, then fire another request
// Cancel polling once condition is met
function* watchPollData() {
  while (true) {
    const { url } = yield take('POLL_FOR_X')
    yield race([
      fork(pollData, url),
      take('POLL_CONDITION_MET')
    ]);
  }
}

// Daemonize tasks in parallel
export default function* root() {
    yield [
        watchPollData()
        // other watchers here
    ];
}

function get(endpoint, tenant) {
  return fetch(endpoint)
  .then(res => res.json())
  .then(json => json)
}

Thanks.

Hi, I believe your code has to be changed to either use call or to change cancel polling management.

    yield race([
      fork(pollData, url),
      take('POLL_CONDITION_MET')
    ]);

Fork immediately resolves, so "POLL_CONDITION_MET" is doing nothing - the saga is being called and forked and we go back up in the loop to wait for take POLL_FOR_X.

https://codepen.io/wjaszczak/pen/pxgVEX?editors=1111 - fork version
https://codepen.io/wjaszczak/pen/xyZjYq?editors=1111 - delegated cancel handling, many active 'polling' methods.