reactive programming with rxjs

RxJS Hands-on

Reactive programming

Reactive extensions for JavaScrips (a.k.a RxJS)

Agenda

What does it mean

to be reactive ?

Before web begin ...

A Reactive system is

One that is in continual interaction with its environment

The Reactive Manifesto

defines reactive as

www.reactivemanifesto.org

scalable

event-driven

resilient

responsive

Reactive programing

A programming paradigm concerned with streams and the propagation of change to simplify the creation of interactive user interfaces and real time system animation

A stream is

A sequence of ongoing events ordered in time

Data streams can be anything :

Arrays, DOM Events, Network request (sockets, Ajax), Animations...

StreamS

[

]

Are like arrays

1s

2s

4s

7s

8s

End

Time

But they can be asynchronous

Error

This is a Data Stream

9

20

8

7

10

Time

Time

This is aN EVENT Stream

Time

This is aN Asynchronous Stream

Data provider (REST API, WebSocket server, ...)

Time

StreamS propagate SIgNALS

Value

Error

completed signal

You need to subscribe to STREAM

And react to new SIGNALS

Streams

could be filtered and concatenated...like any other collection

You can combine streams together to build new ones

Thanks to > Operators

reactive extensions for

JavaScript

RxJS

Key concepts

it's all about OBSERVABLES 

(formerly called streams in reactive programming)

  • A set of any number of things over any amount of time
  • Lazy and juste functions in JavaScript - they don't do anything until you subscribe to them
  • Can be unsubscribed from
  • Are always observed by observers

wait !

how you handle asynchronous calls today ?

promises

promises vs observables

Single value

Multiple value

Not lazy

Cancelable

Lazy

Completion callback

Cannot be cancelled

Catch, Finally

THE GENERAL THEORY OF REACTIVITY

Manual creation of

an observable

const source$ = new Rx.Observable(observer => {
  observer.next('foo');
  observer.next('bar');
  observer.next('baz');
  observer.complete();
});
const source$ = new Rx.Observable.create(observer => {
  observer.next('foo');
  observer.next('bar');
  observer.next('baz');
  observer.complete();
});

you can also Create an observable from something

// From one or multiple values
Rx.Observable.of('foo', 'bar');

// From array of values
Rx.Observable.from([1,2,3]);

// From an event
Rx.Observable.fromEvent(document.querySelector('button'), 'click');

// From a Promise
Rx.Observable.fromPromise(fetch('/users'));

synchronous observables

OBSERVING AN OBSERVABLE

observable

subscription

observer

subscription

observer

OBSERVING AN OBSERVABLE

const source$ = Rx.Observable.of('foo', 'bar', 'baz');
const observer = {
    x => console.log(x),
    err => console.error(err),
    () => console.info('done')
};
source$.subscribe(observer);

Observer is an object with next, error and complete methods

Subscribe to an observable

const subscription = source$.subscribe({
    x => console.log(x),
    err => console.error(err),
    () => console.info('done')
});

to unsubscribe from an observable

const source$ = Rx.Observable(observer => {
    let timeoutId = setTimeout(() => {
        observer.next('You will never see this message');
    }, 2000);
    
    return onUnsubscribe = () => {
        clearTimeout(timeoutId);
    }
});

let subscription = this.data.subscribe(
    value => this.value = value,
    error => console.log(error),
    () => this.status = 'Finished';
);

setTimeout(() => {
  subscription.unsubscribe();
}, 1000);

Define whats to happen on unsubscribe

you should use operators

to compose

new observables

Transforming Observables

Buffer, FlatMap, GroupBy, Map, Scan, Window, ...

Filtering Observables

Debounce, Distinct, Filter, First, Last, Skip, SkipLast, Take ...

Combining Observables

Join, Merge, Switch, Zip, ...

Operators by category

> See documentation

Subjects

A Sub­ject can act as both — a data pro­ducer and a data consumer

Can be sub­scribed to, just like an observ­able

Can sub­scribe to other observables

const observable = Rx.Observable.from([0, 1]);
observable.subscribe(subject);
const subject = new Rx.Subject();

subject.subscribe(v => console.log('consumer A: ' + v));
subject.subscribe(v => console.log('consumer B: ' + v));

subject.next(1);

Hands-on

Clone this project from github

And PUT SOME MUSIC ON

https://goo.gl/3CauDK

install rxjs via npm

npm install rxjs
const { Observable } = require('rxjs/Rx');

Observable.of(1,2,3);

Import only what you need

don't forget to import operators

require('rxjs/add/observable/of');
require('rxjs/add/operator/map');

THANK YOU !

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Reactive Programming with RxJS

By Ouadie LAHDIOUI

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Reactive Programming with RxJS

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