Polling with Observables / RxJs

poll.js

import { Observable } from 'rxjs/Observable';
import { fromPromise } from 'rxjs/observable/fromPromise';
import 'rxjs/add/operator/delay';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/expand';
import 'rxjs/add/operator/takeWhile';
import 'rxjs/add/operator/catch';

const defaultIsComplete = () => false;
const defaultKeepIntervalLow = () => false;
const defaultIntervals = [0, 1000, 1500, 1500, 2000, 2000, 4000, 6000];

const defaultRequest = () => {
    throw new Error('The `request` option is required to start polling.');
};

const poll = (params, options = {}) => {
    const {
        isComplete = defaultIsComplete,
        request = defaultRequest,
        keepIntervalLow = defaultKeepIntervalLow,
        maxAttemps = 15,
        maxPolls = 15,
        intervals = defaultIntervals,
    } = options;

    const initialState = {
        params,
        data: null,
        status: 'started',
        i: 0,
        attemps: 0,
        error: null,
        intervalIndex: 0,
        delay: 0
    };

    const updateDelay = state => {
        const { status, intervalIndex, attemps } = state;
        if (status === 'retry') {
            return {
                ...state,
                intervalIndex: 0,
                delay: Math.pow(2, attemps) * 250
            };
        }
        const intervalIndexNext = keepIntervalLow(state)
            ? state.intervalIndex
            : Math.min(intervalIndex + 1, intervals.length - 1);
        return {
            ...state,
            intervalIndex: intervalIndexNext,
            delay: intervals[intervalIndex]
        };
    };

    return Observable
        .of(initialState)
        .expand(state => {
            const { status, attemps, i } = state;
            if (status === 'completed' || status === 'error') {
                return Observable.of({
                    ...state,
                    status: 'kill'
                });
            }
            if (status === 'retry' && attemps >= maxAttemps) {
                return Observable.of({
                    ...state,
                    status: 'error'
                });
            }
            if (isComplete(state) || i >= maxPolls) {
                return Observable.of({
                    ...state,
                    status: 'completed'
                });
            }

            const stateNext = updateDelay(state);

            return Observable
                .of(stateNext)
                .delay(stateNext.delay)
                .mergeMap(state =>
                    fromPromise(request(state))
                        .map(data => ({
                            ...state,
                            data,
                            status: 'progress',
                            i: state.i + 1,
                            attemps: 0,
                            error: null
                        }))
                        .catch(error => Observable.of({
                            ...state,
                            data: null,
                            status: 'retry',
                            attemps: state.attemps + 1,
                            error
                        }))
                );
        })
        .takeWhile(({ status }) => status !== 'kill');
};

export default poll;

Hi @malte,

Excellent stuff!!!. I needed something like this. I was not able to achieve. For reference please find the below link:
https://stackoverflow.com/questions/51864945/retrying-a-polling-service-with-n-seconds-delay

Do you think we can achieve this with your implementation? Note: We have a pool of polling resources. At one point of time we can poll multiple resources till some condition and on any poll response we have to sync UI respectively.

Thanks in advance
Siddharth