observable_error_failover.js

function getData(){

    var beers = [
        {name: "Stella", country: "Belgium", price: 9.50},
        {name: "Sam Adams", country: "USA", price: 8.50},
        {name: "Bud Light", country: "USA", price: 6.50},
        {name: "Brooklyn Lager", country: "USA", price: 8.00},
        {name: "Sapporo", country: "Japan", price: 7.50}
    ];


    return Rx.Observable.create( observer => {
        let counter = 0;
        beers.forEach( beer => {
                observer.next(beer);
                counter++;

                if (counter > Math.random()*5) {    // Randomly generate an error
                    observer.error(
                        {
                            status: 500,
                            description: "Beer stream error"
                        }
                    );
                } else{
                    emulateDelayInSeconds(1);
                }
            }
        );

        observer.complete();}
    );
}

function emulateDelayInSeconds(seconds)
{
    var e = new Date().getTime() + (seconds * 1000);
    while (new Date().getTime() <= e) {} // just keep the CPU busy
}

// The subscriber
getData()
    .catch(err => {  // failover

        console.error("Got " + err.status + ": " + err.description);
        if (err.status === 500){
            console.error("Switching to streaming cached data");
            return getCachedData();
        } else{
            console.error("Switching to another beer service");
            return getDataFromAnotherService();
        }

    })
    .map(beer => beer.name + ", " + beer.country)
    .subscribe(
        beer => console.log("Subscriber got " + beer),
        err => console.error(err),
        () => console.log("The stream is over")
    );


function getCachedData(){

    var beers = [
        {name: "Leffe Blonde", country: "Belgium", price: 9.50},
        {name: "Miller Lite", country: "USA", price: 8.50},
        {name: "Corona", country: "Mexico", price: 8.00},
        {name: "Asahi", country: "Japan", price: 7.50}
    ];

    return Rx.Observable.create( observer => {

        beers.forEach( beer => {
                observer.next(beer);
                emulateDelayInSeconds(1);
            }
        );

        observer.complete();}
    );
}

function getDataFromAnotherService(){

    var beers = [
        {name: "Peroni", country: "Italy", price: 9.50},
        {name: "Heineken", country: "Holland", price: 8.50},
        {name: "Beck", country: "Germany", price: 8.00},
        {name: "Kingfisher", country: "India", price: 7.50}
    ];

    return Rx.Observable.create( observer => {

        beers.forEach( beer => {
                observer.next(beer);
                emulateDelayInSeconds(1);
            }
        );

        observer.complete();}
    );
}