Rxjs is a library for composing asynchronous and event based programs by using observable sequences. It rovides one core types, the Observables, satellite types ( Observer, Schedules, Subjects ) and operators inspired by Array functions to allow handling asynchronous events as collections.
-
Observer Pattern : The observer pattern is a software design pattern in which an object, called the subject, maintains the list of its dependents, called obsevers, and notifies them automatically of any state change, usually by calling one of their methods.
-
Iterator Pattern : In OOPS, the iterator patters is a design pattern in which an iterator is used to traverse a container and access the container's elements. The iterator pattern decouples algorithms from containers, in some cases, algorithms are necessarily container-specific and thus cannot be decoupled.
-
Pure Functions : A pure function is deterministic. This means, that given the same input, the function will always return the same output.
ReactiveX combines Observer pattern with the iterator pattern and functional programming with collections to fill the need for an ideal way of managing sequence of events.
The essential concepts in RxJs which solve async event management are:
- Observable: represents the idea of an invokable collection of future events.
- Observer: is a collection of callbacks that knows how to listen to values delivered by the Observable.
- Subscription: represents the execution of an observable, is primarily useful for cancelling the execution.
- Operators: are pure functions that enable a functinal programming style of dealing with collections with operators like map, filter, concat, etc.
- Subject: is the equivalent to an EventEmitter, and the only way of multicasting a value or event to multiple observers.
- Schedulers: are centralized dispatchers to control concurrency, allowing us to coordinate when computation happends on eg. setTimeout or others.
var button = document.querySelector('button');
button.addEventListener( 'click', () => console.log());
Using Rxjs you create an observable instead.
var button = document.querySelector('button');
Rx.Observable.fromEvent( button, 'click' )
.subscribe(() => console.log('Clicked!'));
Streams are just a sequence of values over time. Reactive programming is the idea that we can define an application as a series of different streams with an operation that connects different streams together and which are automatically called when new values are pushed into those streams.
Observables are blue prints for creating streams and plumbing them together with operators to create observables chain
By default, Observables are cold and only gets hot when you subscribe to them.
What makes Rxjs powerful is the ability to produce values using pure functions. That means your code is less prone to errors. Normally you would create an impure function, where other pieces of your code can mess up your state.
var count = 0;
var button = document.querySelector('button');
button.addEventListener('click', () => console.log(`Clicked ${ ++count } times` ));
But using Rxjs, you isolate the state.
var button = document.querySelector('button');
Rx.Observable.fromEvent( button, 'click' )
.scan( count => count + 1, 0 )
.subscribe( count => console.log( count ));
The scan opeator acts just like the reduce for arrays. It takes a value which is exposed to a callback. The returned value of the callback will then become the next value exposed the next time the callback runs.__
Rxjs has a whole range of operators that helps you control how the events flow through your observables. This is how you would allow at most one click per second.
var count = 0;
var rate = 1000;
var lastClick = Date.now() - rate;
var button = document.querySelector('button');
button.addEventListener( 'click', () => {
if( Date.now() - lastClick >= rate ){
console.log( `Clicked ${ ++count } times `);
lastClick = Date.now();
}
});
with RxJS
var button = document.querySelector('button');
Rx.Observable.fromEvent(button, 'click')
.throttleTime(1000)
.scan(count => count + 1, 0)
.subscribe(count => console.log(`Clicked ${count} times`));
other flow control operators are filter, delay, debounceTime, take, takeUntil, distinct, distinctUntil
for usage in angular projects on a button with a click event
private clickSubject = new Subject<void>();
ngOnInit() {
this.clickSubject.pipe(
throttleTime( 1000 ),
scan((count, val) => count + 1, 0 ),
).subscribe(
count => console.log( count )
)
this.clickSubject.subscribe(() => {
console.log('clicked');
});
}
onClick() {
this.clickSubject.next();
}
You can transform the values passed through your observables.
Rx.Observable.fromEvent( button, 'click' )
.throttleTime( 1000 )
.map( event => event.clientX )
.scan(( count, clientX ) => count + clientX, 0 )
.subscribe( count => console.log( count ));
Other value producing operators are pluck, pairwise, sample etc
Observables are lazy push collections of multiple values. They fill the missing spot in the following table.
| Single | Multiple | |
|---|---|---|
| Pull | Function | Iterator |
| Push | Promise | Observable |
var observable = Rx.Observable.create(( observer ) => {
observer.next(1);
observer.next(2);
observer.next(3);
setTimeout(() => {
observer.next(4);
observer.complete();
}, 1000);
});
The observable that pushes the values 1,2, 3 immediately ( synchronously ) when subscribed, and the value 4after one second has passed since the subscribe call, then completes. To invoke the observable and see these values, we need to subscribe to it.
var observable = Rx.Observable.create(( observer ) => {
observer.next(1);
observer.next(2);
observer.next(3);
setTimeout(() => {
observer.next(4);
observer.complete();
}, 1000);
});
console.log('just before the subscribe')l
observable.subscribe({
next: x=> console.log('something wrong occured: ' + err ),
error: err => console.error('something wrong occured: ' + error ),
complete: () => console.log('done'),
});
console.log('just after subscribe');
Pull and Push are two different protocols that describes how a data Producer can communicate with a data consumer.
In Pull Systems, the consumer determines when it receives data from the data producer. The producer itself is unware of when the data will be delivered to the consumer. Every JavaScript function is a pull system. The function is a producer of data, and the code that calls the function is consuming it by "pulling" out a single return value from its call.
| Producer | Consumer | |
|---|---|---|
| Pull | Passive: producers data when requested. | Active: decides when data is requested. |
| Push | Active: produces data at its own pace. | Passive: reacts to receive data. |
In Push system, the producer determines when to send data to the consumer. The consumer is unaware of when it will receive data.
Promises are the most common type of Push System. A Promise delivers a resolved value to registered callbacks, but unlike functions, it is the Promise whoch is in charge of determining precisely when the value ois "pushed" to the callbacks.
RxJS introduces Observables, a new push system for javascript. An Observable is a Producers of multiple values, "pushing" them to Observers.
- A Function is a lazily evaluated computation that synchronously returns a single value on invocation.
- A generator is a lazily evaluated computation that synchronously return zero to infinite values on iteration.
- A Promise is a computation that may or may not eventually return a single value.
- An Observable is a lazily evaluated computation that can synchronously or asynchronously return zero to infinite values from the time it's invoked onwards.
Contrary to popular claims, Observables are not like EventEmitters not are they like Promises for mulitple values. Obervables may act like EventEmitters in some cases, namely when they are multicasted using RxJs Subjects, but usually they don't act like eventEmitters. Observables are liek functions with zero argument, but generalize those to allow multiple values.
var foo = Rx.Observable.create(( observer ) => {
console.log('Hello')
observer.next( 42 );
});
foo.subscribe((x) => {
onsole.log(x);
})
foo.subscribe((y) => {
console.log(y);
})
Output:
"Hello"
42
"Hello"
42
This happens because both functions and observables are lazy computations. If you dont call the function, the console.log('Hello') won't happen. Also with Observables, if you don't "call" it, the console.log('Hello') won't happen. Plus, "calling" or "subscribing" is an isolated operation: two function calls trigger two separate side effects, and two Observables subscribes trigger two separate side effects. As Opposed toe EventEmitters which share the side effects and have eager execution regardless of the existence of subscribers, Observables have no shared execution and are lazy.
What is the difference between an Observable and a function? Observables can "return" mulitple values over time, something which functiona cannot.
Funtions can return only one value. Observables, how ever can do this.
var foo = Rx.Obsevables.create(( observer ) => {
console.log('Hello');
observer.next(42);
observer.next(100); // return another value
observer.next(200); // return yet another
setTimeout(() => {
observer.next(300); // async
}, 3000)
});
console.log('before');
foo.subscribe((x) => {
console.log(x);
});
console.log('after');
Output:
"before"
"Hello"
42
100
200
"after"
300
- function.call() means "give me one value synchronously".
- Observable.subscribe() means "give me any amount of values, either synchronously or asynchronously
Observables are created using Rx.Observable.create or a creation operation, are subscribed to with an Observer, execute to deliver next/error/complete notifications to the observer, and their execution may be disposed.
Core Observables concerns:
- Creating Observables
- Subscribing Observables
- Executing the Observables
- Disposing Observables
Rx.observable.create si an alias for the Observable constructor, and takes one argument: the subscribe function.
var observable = Rx.Observable.create(( observer ) => {
var id = setInterval(() => {
observer.next('hi');
}, 1000);
})
Observables can be created with create, but usually we use the so-called creation operators, like of, from, interval, etc.
The Observable observable in the example can be subscribed to, like this:
observable.subscribe( x => console.log( x ));
Its not a conincidence that observable.subscribe and subscribe in Observable.create(function subscribe( observer ){...}) have the same name. In the library, they are different, but for practical purposes you can consider them conceptually equal. This shows that subscribe calls are not shared among multiple Observers of the same Observable. When calling observable.subscribe with an Observer, the function subscribe in Observable.create( function subscribe( observer ){ ... }) is run for that Observer. Each call to observable.subscribe triggeres its own independent setup for that given Observer.
Subscribing to an observable is like calling a function, providing callbacks where the data will be deivered to.
A subscribe call is a simply a way to start an Observable execution and deliver values or events to an Observer of the execution.
The code inside Observable.credate( function subscribe( observer ){ ... }) represents an 'Observable execution`, a lazy computation that only happends for each Observer that subscriber. The execution producers multiple values over time, either synchronously or asynchronously.
There are three types of values on Observable Execution can deliver:
- Next notification: sends a value such as a number, a string, an object etc.
- Error notification: sends a javascript error or exception.
- Complete notification: does not send a value.
Next notifications are expressed best in the so-called Observable Grammer or contract, written as a regular expression:
next*( error | complete )?
In an Observable Execution, zero to infinite Next notification may be delivered. If either an Error or complete notification is delivered, then nothing else can delivered afterwards.
var observable = Rx.Observable.create( function subscribe( observer )){
observer.next(1);
observer.next(2);
observer.next(3);
observer.complete();
observer.next(4); // Is not delivered because it would violate the contract
});
It is a good idea to wrap any code in subscribe with try/catch block that will deliver an Error notification if it catches an exception:
var observable = Rx.Observable.create( function subscribe( observer ){
try{
observer.next(1);
observer.next(2);
observer.next(3);
observer.complete();
}catch( err ){
observer.error( err );
}
})
Because Observable Executions may be infinite, and it's common for an Observer to want to abort execution in finite time, we need an API for cancelling an execution . Since each execution is exclusive to one observer only, once the Observer is done receiving values, it has to have a way to stop the execution, in order to avoid wasting compution power or memory resources. When observable.subscribe is called, the observer gets attached to the newly create Observable execution. This call also returns an object, the subscrition.
var subscription= observable.subscrie( x => console.log( x ));
The subscription representsthe ongoing execution, and has a minimal API which allows you to cancel the execution. with subscription.unsubscribe you can cancel the ongoing execution.
var observable = Rx.Observable.from([ 10, 20, 30 ]);
var subscription = observable.subscribe( x => console.log(x));
subscription.unsubscribe();
When you subscribe, you get back a subscription, which represents the ongoing execution. Just call unsubscrieb() to cancel the execution.
Each observable must define how to dispose resouces of that execution when we create the Observable using create(). You can dot hat by returning a custom unsubscribe function from within function subscribe().
var observable = Rx.Observable.create( function subscribe( observer ){
var intervalId = setInterval(() => {
observer.next('hi);
}, 1000);
return function unsubscribe(){
clearInterval( intervalID );
}
})
Just like observable.subscribe resembles Observable.create(function subscribe() {...}), the unsubscribe we return from subscribe is conceptually equal to subscription.unsubscribe. In fact, if we remove the ReactiveX types surrounding these concepts, we're left with rather straightforward JavaScript.
function subscribe(observer) {
var intervalID = setInterval(() => {
observer.next('hi');
}, 1000);
return function unsubscribe() {
clearInterval(intervalID);
};
}
var unsubscribe = subscribe({next: (x) => console.log(x)});
// Later:
unsubscribe(); // dispose the resources
An observer is a consumer of vlaues delivered by an Observable. Observers a simply a set of callbacks, one for each type of notification delivered by the Observable: next, error, and complete. example
var observer = {
next: x => console.log('Observer got a next value: ' + x ),
error: err => console.log('Observer got an error : ' + err ),
complete: () => console.log('Observer got a complete notification'),
};
Observers are just objects with three callbacks, one for each type of notification that an observable may deliver.
Observers in Rxjs may also be partial. If you don't provide one of the callbacks, the execution of the observable will still happend normally, except some of types of notifications will be ignored because they don't have corresponding callback in the observer. When subscribing to an observable you may also just provide the callbacks as an arguments, without being attached to an Observer object, for instance
observable.subscribe(x => console.log('Observer got a next value: ' + x));
Internally in observable.subscribe, it will create an observer object using the first callback argument as the next handler. All three types of callbacks may be provided as arguments:
observable.subscribe(
x => console.log('Observer got a next value: ' + x),
err => console.error('Observer got an error: ' + err),
() => console.log('Observer got a complete notification')
);
A subscription is an object that represents a disposable, resource, usually the execution of an observable. A Subscription has one important method, unsubscribe, that makes no argument and just disposed the resource help by the subscription.
A Subscription essentially just has an unsubscribe() function to release resources or cancel observable executions.
Subscriptions can also be put together, so that a call to an unsubscribe() of one subscription may unsubscribe mulitple subscriptions.
var observable1 = Rx.observable.interval( 300 );
var observable2 = Rx.observable.interval( 300 );
var subscription = observable1. subscribe( x => console.log( 'first: ' + x));
var childSubscription = observable2.subscribe( x => console.log('second: ' + x ));
subscription.add( childSubscription );
setTimeout(() => {
subscription.unsubscribe();
}, 1000);
Subscription also have a remove( otherSubscription ) method inorder to undo the adition of a child subscription.
An Rxjs Subject is a special type of observable that allows values to be multicasted to many observers. While plain observables are uncast, subjects are multicast.
A Subject us like an observable, but can multicast to many observers. Subjects are like EventEmitters: they miantain a registry of many listeners.
Every Subject is an observable - Given a subject, you can subscribe to it, providing an observer, which will start receiving values normally. From the prespective of the observer, it cannot tell whether the observable execution is coming from a plain unicast Observable or a subject. Internally to the subject, subscribe does not invoke a new execution that delivers values. It simply registers the given observer in a list of observers, similarly to how addListener usually works in other libraries and language.
Every Subject is an Observer - It is an object with the methods next(v), error(e) and complete(). To feed a new value to the subject, just call the next(value), and it will be multicasted to the observers registered to listen to the subject.
var subject = new Rx.Subject();
subject.subscribe({
next: (v) => console.log( 'observableA: ' + v )
});
subject.subscribe({
next: (v) => {
console.log( 'observerB)
}
});
subject.next(1);
subject.next(2);
Since a subject is an Observer, this also means you may provide a Subject as the argument to the subscribe of any Observable, like the example below shows:
var subject = new Rx.Subject();
subject.subscribe({
next: (v) => console.log( 'observeA: ' + v )
});
subject.subscribe({
next: (v) => console.log( 'observeB' + v )
});
var observable = Rx.Observable.from([1, 2, 3]);
observable.subscribe( subject );
There are also a few specializations of the Subject type: BehaviorSubject, and AsyncSubject.
A "multicaster Observable" passes notifications through a Subject which may have many subscribes, whereas a plain "unicast Observable" only sends notifications to a single observer.
A multicasted Observable uses a subject under the hood to make multiple observers see the same Observable execution.
Observers subscribe to anunderlying Subject, and the Subject subscribe to the sources observable.
var source = Rx.Observable.from([1, 2, 3]);
var subject = new Rx.Subject();
var multicasted = source.multicast( subject );
multicasted.subscribe({
next: (v) => console.log( 'observerA: ' + v )
});
multicasted.subscribe({
next: (v) => console.log( 'observerB: ' + v)
});
multicasted.connect();
multicast returns an Observable that looks like a normal Observable, but works like a Subject when it comes to subscribing. multicast returns a ConnectableObservable, which simple an Observable with the connect() method. The connect() method is important to determine exactly when the shared Observable exxecution will start. Because connect() does source.subscribe( subject ) under the hood, connect() returns a Subscription, which you can unsubscribe from the in order to cancel the shared Observable execution.
Calling connect() manually and handling the Subscription is often cumbersome. Usually, we want to automatically connect when the first Observer arrives, and automatically cancel the shared execution when the last Observer unsubscries.
Conside the following example where subscriptions occur as outlines by this list.
- First Observer subscribes to the multicasted Observable
- The multicasted Observable is connected.
- The next value 0 is delivered to the multicasted Observable.
- Second Observer subscribes to the multicasted Observable.
- The next value 1 is delivered to the first Observer.
- The next value 1 is delivered to the second observer.
- First Observer unsubscribes from the multicasted Observable.
- The next value 2 is delivered to the second Observer.
- Second Observer unsubcribes from the multicasted Observable.
- The connection to the multicasted Observable is unsubscribed.
var source = Rx.Observable.interval( 500 );
var subject = new Rx.Subject();
var multicasted = source.multicast( subject );
var subscription1, subscription2, subscriptionConnect;
subscription1 = multicasted.subscribe({
next: (v) => console.log( 'observerA: ' + v )
});
subscriptionConnect = multicasted.connect();
setTimeout(() => {
subscription2 = multicasted.subscribe({
next: (v) => console.log( 'observerB: ' + v)
});
}, 600 );
setTimeout(() => {
subscription1.unsubscribe();
}, 1200);
setTimeout(() => {
subscription2.unsubscribe();
subscriptionConnect.unsubscribe();
}, 2000);
If we wish to avoid explicit calls to connect(), we can use ConnectableObservable's refCount() method, which returns an Observable that keep track of how many subscribes it has. When the number of subscribers increases from 0 to 1, it will call connect() for us, which starts the shared execution. Only when number of subscribers decreases from 1 to 0 will it be fully unsubscribed, stopping further execution.
var source = Rx.Observable.interval(500);
var subject = new Rx.Subject();
var refCounted = source.multicast(subject).refCount();
var subscription1, subscription2, subscriptionConnect;
// This calls `connect()`, because
// it is the first subscriber to `refCounted`
console.log('observerA subscribed');
subscription1 = refCounted.subscribe({
next: (v) => console.log('observerA: ' + v)
});
setTimeout(() => {
console.log('observerB subscribed');
subscription2 = refCounted.subscribe({
next: (v) => console.log('observerB: ' + v)
});
}, 600);
setTimeout(() => {
console.log('observerA unsubscribed');
subscription1.unsubscribe();
}, 1200);
// This is when the shared Observable execution will stop, because
// `refCounted` would have no more subscribers after this
setTimeout(() => {
console.log('observerB unsubscribed');
subscription2.unsubscribe();
}, 2000);
output
observerA subscribed
observerA: 0
observerB subscribed
observerA: 1
observerB: 1
observerA unsubscribed
observerB: 2
observerB unsubscribed
The refCount() method only exists on ConnectableObservable, and it returns an Observable, not another ConnectableObservable.
One of the variants of Subjects is the BehaviorSubject, which has a notion of "the current value". It stores the latest value emiited to its consumers, and whenever a new Observer subscries, it will immediately receive the "current value" from the BehaviorSubject.
BehaviorSubject are useful for representing "value over time". For instance, an event stream of birthdays is a subject, but the stream of a person's age would be a BehaviorSubject.
The BehaviorSubject is initialized with the value 0 which the first Observer receives when it subscribes. The second observer receives the value 2 even though it subscribed after the value 2 was sent.
var subject = new Rx.BehvaiorSubject(0);
subject.subscribe({
next: (v) => console.log('observerA : ' + v )
});
subject.next(1);
subject.next(2);
subject.subscribe({
next: (v) => console.log('observerB: ' + v )
});
subject.next(3);
Output:
observerA: 0
observerA: 1
observerA: 2
observerB: 2
observerA: 3
observerB: 3
A ReplaySubject is similar to a BehaviorSubject in that it can send old values to new subscribers, but it can also record a part of the Observable execution. When creating a ReplaySubject, you can specify how many values to replay.
A ReplaySubject records multiple values from the observable execution and replays them to new subscribers
var subject = new Rx.ReplaySubject(3);
subject.subscribe({
next: (v) => console.log( 'observerA: ' + v )
});
subject.next(1);
subject.next(2);
subject.next(3);
subject.next(4);
subject.subscribe({
next: (v) => console.log('observerB: ' + v )
});
subject.next(5);
output:
observerA: 1
observerA: 2
observerA: 3
observerA: 4
observerB: 2
observerB: 3
observerB: 4
observerA: 5
observerB: 5
The AsyncSubject is a variant where only the last value of the Observable execution is sent to its observers, and only when the execution completes.
var subject = new Rx.AsyncSubject();
subject.subscribe({
next: (v) => console.log( 'observerA: ' + v );
})
subject.next(1);
subject.next(2);
subject.next(3);
subject.next(4);
subject.subscribe({
next: (v) => console.log( 'observerB' : + v );
});
subject.next( 5 );
subject.complete();
The AsyncSubject is similar to the last() operatorm in that it waits for the complete notification in order to deliver a single value.
Rxjs is mostly useful for its operators, even though the Observable is the foundation. Operators are the essential pieces that allow complex asynchronous code to be easily composed in a declarative manner.
An Operator is a function which creates a new Observable based on the current Observable. This is a pure operation.
An operator is essentially a pure function which takes one Observable as input andd generates another Observable as output. Subscribing to the output observable will also subscribe to the input Observable. In the following example, we create a custom operator function that multiplies each value received from the input Observable by 10:
function multiplyBy10( input ){
var output = new Rx.Observable.create( function subscribe( observer ){
input.subscribe({
next: (v) => observer.next( 10 * v ),
error: ( err ) => observer.error( err ),
complete: () =? observer.complete()
});
});
return output;
}
var input = Rx.Observable.from([1,2,3,4,5]);
var output = multiplyBy10( input );
output.subscribe( x => console.log( x ));
output:
10
20
30
40
Instance operators are fucntion that use this keyword to infer what is the input observable.
Static operators are pure functions attached to the Observable class, and usaully are used to create Observables from scratch.
The most common type of static operators are the so-called Creation Operators. Instead of transforming an input Observable, they simply take a non-Observable argument,and create a new Observable. A typical example fo a static creation operator would be the interval function.It takes a number as an input argument and produces an Observable as output.
var observable = Rx.Observable.interval(1000 /* number of milliseconds */);
Static operators may be of different nature than simply creation. Some Combination Operators may be static, such as merge, concat etc. These makes sense as static operators because they take multiple Observables as input.
var observable1 = Rx.Observable.interval( 1000 );
var observable2 = Rx.Observable.interval( 400 );
var merged = Rx.Observable.merge( observable1, observable2 );
To expalin how operators work, textual descriptions are often not enough. Many operators are related to time, they may for instance delay, sample, throttle, or debounce value emission in different ways. Diagrams are often a better tool for that. Marble Diagrams are visual representations of how operators work, and include Observables, the operator and its parameterm and the output Observable.
In a marble diagram, time flows to the right, and the diagram describes how values ("marbles") are emitted on the Observable execution.
There are operators for different purposes, and they may be categorized as: creation, transformation, filtering, combination, multicasting, error handling, utility etc.
- Creation Operators
- Transformation Operators
- Filtering Operators
- Combination Operators
- Mulitcating Operators
- Error Handling Operators
- Utility Operators
- Conditional and Boolean Operators
- Mathmatical and Aggregate operators
A Scheduler controls when a subscription starts and when notifications are delivered. It consists of three components.
- A Scheduler is a data structure - It knows how to store and queue tasks based on priority or other criteria.
- A Scheduler is an execution context - It denotes where and when the task is executed.
- A Schedule has a ( virtual ) clock - It provides a notion of "time" by a getter method now() on the Scheduler. Task being scheduled on a particular sceduler will adhere only to the time denoted by the clock.
A Scheduler lets tou define in what execution context will an observable deliver notifications to its observer.
var observable = Rx.Obseevable.create( function( observer ){
observer.next(1);
observer.next(2);
observer.next(3);
observer.complete();
})
.observeOn( Rx.Scheduler.async );
console.log( 'just before subscribe' );
observable.subscribe({
next: x => console.log( 'got value' + x ),
error: err => console.log( err ),
complete: () => console.log('done'),
});
console.log('just after subscribe');
Output:
just before subscribe
just after subscribe
got value 1
got value 2
got value 3
done
var button = document.querySelector( 'button' );
var osberver = {
next: function( value ){
console.log( value );
},
error: function( error ){
console.log( error )
},
complete: function(){
console.log( 'Completed' );
}
};
// Rx.Observable.fromEvent( button, 'click' )
// .subscribe( observer );
var subscription = Rx.Observable.create(( obs ) => {
obs.next( 'A Value' );
setTimeout(() => {
obs.complete();
}, 3000)
obs.next( 'A second value' );
}).subscribe( observer );
setTimeout(() => {
subscription.unsubscribe();
}, 5000 );
var observable = Rx.Observable.interval( 1000 );
var observer = {
next: function( value ){
console.log( value );
};
}
observable.subscribe( observe );
Buffers the source Observable values until closingNotifiers emits.
- Paramateres:
closingNotifier: An Observable that signals the buffer to be emitted on the output observable.
- Returns :
OperatorFunction<T, T[]>: An Observable of buffers, which are arrays of values.
- Description :
Collects value from the past as an array, and emits that array only when observable emits.
Buffers the incoming Observable values until the given closingNotifier Observable emits a value, at which point it emits the buffer on the output Observable and starts a new buffer internally, awaiting the next time closingNotifier emits.
- Exmaple:
const clicks = fromEvent( document, 'click' );
const interval = interval( 1000 );
const buffered= interval.pipe( buffer( clicks ));
buffered.subscribe( x => console.log( x ));
- Parameters
selector: Type:
( err: any, caught: Observable ) => ObservableInput.
- Returns
OperatorFunction<T, T | R>
Flattens all the Observable of Observable by applying
combinelatestwhen the Observable-of-Observable completes.
- Parameters
Project: Optional. Default is
undefined
- Returns
OperatorFunction<T, R>:
- Description
combineAll takes an Observavble of Observable, and collects all Observable from it. Once the outer Observable completes, it subscribes to all Collected Observables and combines their values using the combineLatest strategy such that:
-
Every time an inner Observable emits, the output Observable emits
-
When the returned observable emits, it emits all of the latest values by:
- If a
projectfunction is provided, it is called with each recent value from each inner Observable in whatever order they arrived, and the result of theprojectfunction is what is emitted by the output Observable. - If there is no
projectfunction, an array of all the most recent values is emitted by the output Observable.
- If a
-
Exmaple
const clicks = fromEvent( document, 'click' );
const higherOrder = clicks.pipe(
map( ev =>
interval( Math.random() * 2000 ).pipe( take( 3 ))
),
take( 2 )
);
const result = higherOrder.pipe(
combineAll()
);
result.subscribe( x => console.log( x ));