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[RxJS] Subject: an Observable and Observer hybrid
This lesson teaches you how a Subject is simply a hybrid of Observable and Observer which can act as a bridge between the source Observable and multiple observers, effectively making it possible for multiple observers to share the same Observable execution.
var observable = Rx.Observable.interval(1000).take(5);var observerA = { next: function (x) { console.log(‘A next ‘ + x); }, error: function (err) { console.log(‘A error ‘ + err); }, complete: function () { console.log(‘A done‘); },};var observerB = { next: function (x) { console.log(‘B next ‘ + x); }, error: function (err) { console.log(‘B error ‘ + err); }, complete: function () { console.log(‘B done‘); },};observable.subscribe(observerA);setTimeout( () => { observable.subscribe(observerB); },2000)
In the code above, we have two ‘observers‘, because we call subscribe twice:
observable.scbscribe(ObserverA);observable.scbscribe(ObserverB);
If we want to have one observer, so we need to call subscribe only once.
For that we can build a bridgeObservers, which will loop though the observers:
const observable = Rx.Observable.interval(1000).take(5);const ObserverA = { next: function(x){ console.log("A next " + x) }, error: function(x){ console.error("A error " + x) }, complete: function(){ console.log("A Done") },};const ObserverB = { next: function(x){ console.log("B next " + x) }, error: function(x){ console.error("B error " + x) }, complete: function(){ console.log("B Done") },};const BridgeObservers = { next: function(x){ this.observers.forEach( o => o.next(x) ) }, error: function(x){ this.observers.forEach( o => o.error(x) ) }, complete: function(){ this.observers.forEach( o => o.complete() ) }, observers: [], addObserver: function(observer){ this.observers.push(observer) }};observable.subscribe(BridgeObservers);BridgeObservers.addObserver(ObserverA);setTimeout(function(){ BridgeObservers.addObserver(ObserverB);}, 2000)
And this partten:
observable.subscribe(BridgeObservers);BridgeObservers.addObserver(ObserverA); // BirdegeObservers.subscribe(ObserverA)is actually ‘subject‘ partten, works both as Observer and Observable.
Subject:
const observable = Rx.Observable.interval(1000).take(5);const ObserverA = { next: function(x){ console.log("A next " + x) }, error: function(x){ console.error("A error " + x) }, complete: function(){ console.log("A Done") },};const ObserverB = { next: function(x){ console.log("B next " + x) }, error: function(x){ console.error("B error " + x) }, complete: function(){ console.log("B Done") },};const subject = new Rx.Subject();/*const BridgeObservers = { next: function(x){ this.observers.forEach( o => o.next(x) ) }, error: function(x){ this.observers.forEach( o => o.error(x) ) }, complete: function(){ this.observers.forEach( o => o.complete() ) }, observers: [], subscribe: function(observer){ this.observers.push(observer) }};*/observable.subscribe(subject);subject.subscribe(ObserverA);//BridgeObservers.subscribe(ObserverA);setTimeout(function(){ subject.subscribe(ObserverB); // BridgeObservers.subscribe(ObserverB);}, 2000)
In the end, ObserverA and ObserverB share one single observer.
[RxJS] Subject: an Observable and Observer hybrid
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