Observable

observable.js

function myUpload (url, file) {
    return new Observable(subscriber => {
        const request = new XMLHttpRequest();
        request.onload = function(data) {
            subscriber.next(data);
            subscriber.complete();
        }
        request.onerror = function(error) {
            subscriber.error(error);
        }
        request.send();
        return function() {
            request.abort();
        }
    });
}

const uploadObservable = myUpload('', file);

const uploadSubscription = upload.subscribe({
    next: () => {}
})

const uploadSubscription2 = upload.subscribe({
    next: () => {}
})

button.addEventListener('click', uploadSubscription.unsubscribe);



function getEventStream(eventType) {
    const observers = [];

    const handler = event => {
        console.log('log');
        observers.forEach(observer => observer.next(event));
    }

    return new Observable(observer => {
        observers.push(observer);
        
        if (observers.length === 1) {
            document.addEventListener(eventType, handler);
        }
        return () => {
            observers.remove(observer);
            if (observers.length === 0) {
                document.removeEventListener(eventType, handler);
            }
        }
    });
}

const clicks = getEventStream('click');

simulateClick(); // 

const sub = clicks.subscribe({
    next: () => { console.log() }
});

simulateClick(); // log

const subscription = [0,1,2,3,4].map(
    () => clicks.subscribe({
        next: () => { console.log() }
    })
);

simulateClick(); // log

subscription[0].unsubscribe();
simulateClick(); // log
subscription[1].unsubscribe();
simulateClick(); // log
subscription[2].unsubscribe();
simulateClick(); // log
subscription[3].unsubscribe();
simulateClick(); // log
subscription[4].unsubscribe();

simulateClick(); //