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function multicastSequenceSubscriber() {
const seq = [1, 2, 3];
// Keep track of each observer (one for every active subscription)
const observers = [];
// Still a single timeoutId because there will only ever be one
// set of values being generated, multicasted to each subscriber
let timeoutId;
*
// Return the subscriber function (runs when subscribe()
// function is invoked)
return (observer) => {
observers.push(observer);
// When this is the first subscription, start the sequence
if (observers.length === 1) {
timeoutId = doSequence({
next(val) {
// Iterate through observers and notify all subscriptions
observers.forEach(obs => obs.next(val));
},
complete() {
// Notify all complete callbacks
observers.forEach(obs => obs.complete());
}
}, seq, 0);
}
*
return {
unsubscribe() {
// Remove from the observers array so it's no longer notified
observers.splice(observers.indexOf(observer), 1);
// If there's no more listeners, do cleanup
if (observers.length === 0) {
clearTimeout(timeoutId);
}
}
};
};
}
*
// Run through an array of numbers, emitting one value
// per second until it gets to the end of the array.
function doSequence(observer, arr, idx) {
return setTimeout(() => {
observer.next(arr[idx]);
if (idx === arr.length - 1) {
observer.complete();
} else {
doSequence(observer, arr, idx++);
}
}, 1000);
}
*
// Create a new Observable that will deliver the above sequence
const multicastSequence = new Observable(multicastSequenceSubscriber);
*
// Subscribe starts the clock, and begins to emit after 1 second
multicastSequence.subscribe({
next(num) { console.log('1st subscribe: ' + num); },
complete() { console.log('1st sequence finished.'); }
});
*
// After 1 1/2 seconds, subscribe again (should "miss" the first value).
setTimeout(() => {
multicastSequence.subscribe({
next(num) { console.log('2nd subscribe: ' + num); },
complete() { console.log('2nd sequence finished.'); }
});
}, 1500);
*
// Logs:
// (at 1 second): 1st subscribe: 1
// (at 2 seconds): 1st subscribe: 2
// (at 2 seconds): 2nd subscribe: 2
// (at 3 seconds): 1st subscribe: 3
// (at 3 seconds): 1st sequence finished
// (at 3 seconds): 2nd subscribe: 3
// (at 3 seconds): 2nd sequence finished |
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