Observable from rxjs

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According to this topic: What is the difference between Promises and Observables?

It was said there by many users that Observable is like a stream. It is really hard to me to understand, how particular endpoint for example this one:

https://jsonplaceholder.typicode.com/posts

can returns many values over time. Since it is http request a single resposne is returned no matter if it was succeed or failed.

You are correct, an http request will still only return a single event when using it with observables. So if the only asyncronous operation you are doing is a single http request, there is no benefit from using an observable over a promise.

The power of RxJS and observables comes when you start combining several observable streams together. This can be done with operators like mergeMap, switchMap, forkJoin, combineLatest, etc. When you start doing this you can get a lot of benefits from having your http requests as observables.

Take polling for example, creating an event stream that fires every 10 seconds and then polls the server with an http request is a use case where doing http requests with observables really shines.

from, from converts various other objects and data types into Observables. It also converts a Promise, an array-like, or an iterable object into an Observable that emits� An Observable is a Producer of multiple values, "pushing" them to Observers (Consumers). A Function is a lazily evaluated computation that synchronously returns a single value on invocation. A generator is a lazily evaluated computation that synchronously returns zero to (potentially) infinite values on iteration.

Observables are useful when we want to manage and/or combine multiple events over time.

Lets imagine we have a method will return a promise for that JSON:

const dataPromise = fetchData('https://jsonplaceholder.typicode.com/posts');

Also, imagine that we're tracking user presence on the current page:

const userLeavePromise = trackUserPresence();

Lets now draw timelines for the data fetching and user leaving events. Here o stands for event, happening in time:

            1s  2s  3s  4s  5s
data        ------------o
userLeave   --------o

For example sake, data would be fetched at 4th second, while our restless user would leave the page at 3rd. In this case we want to cancel the fetch operation and all post-processing callbacks (in Promise terms, all .then-ned functions).

For such (and many more) situations RxJS provides lots of operators that let us combine events over time.

In this particular case we would take data, Until user leaves the page:

// Observable for data
const data$ = fetchData('https://jsonplaceholder.typicode.com/posts');

// Observable for user leave
const userLeave$ = trackUserPresence();

data$
  .takeUntil(userLeave$)
  .subscribe(data => console.log(data))

The RxJS library, Composing multiple streams. Observable creation functionslink. RxJS offers a number of functions that can be used to create new observables. These functions � RxJS - Observables - An observable is a function that creates an observer and attaches it to the source where values are expected from, for example, clicks, mouse events from a dom Home Jobs

Comparing http request by a promise and observable is not much different because the observable completes once the request is done so it is not a long lived observable. But the one below emits each time you click the button.

const { fromEvent } = rxjs;

fromEvent(document.getElementById('clickMe'), 'click').subscribe(() => { 
  console.log('clicked button');
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/6.4.0/rxjs.umd.min.js"></script>
<button id="clickMe">Click me</button>

Turn an array, promise, or iterable into an observable., This operator can be used to convert a promise to an observable! For arrays and iterables, all contained values will be emitted as a sequence! const observable = Rx.Observable.forkJoin( Rx.Observable.interval(1000).take(3), // emit 0, 1, 2 every second and complete Rx.Observable.interval(500).take(4), // emit 0, 1, 2, 3 every half a second and complete (n, m) => n + m ); observable.subscribe( value => console.log(value), err => {}, () => console.log('This is how it ends!')

Observable, Creates an Observable that emits sequential numbers every specified interval of time, on a specified IScheduler. public static. merge(observables: Redux-Observable is an RxJS-based middleware for Redux that allows developers to work with async actions. It's an alternative to redux-thunk and redux-saga. This article covers the basics of RxJS, how to setup Redux-Observables, and some of its practical use-cases. But before that, we need to understand the Observer Pattern.

Understanding RxJS Observables and why you need them , Streams are important to understand because they are facilitated by RxJS Observables. An Observable is basically a function that can return a stream of values to an observer over time, this can either be synchronously or asynchronously. The data values returned can go from zero to an infinite range of values. The Angular Observable tutorial covers how to use RxJS Observables in Angular application. When we talk about Angular Observable, we hear a lot of terms like Reactive programming, data streams, Observable, Observers, RxJS, etc. It is very important to understand these terms before we start using the observables Rx stands from Reactive programming.

Observables & RxJS • Angular, Observables are a blueprint for creating streams and plumbing them together with operators to create observable chains. RxJS is a library that lets us create and� Observables are a blueprint for creating streams and plumbing them together with operators to create observable chains. RxJS is a library that lets us create and work with observables. We can subscribe to an observable chain and get a callback every time something is pushed onto the last stream.

Comments
  • Well, it's a stream with one value. It's still a stream. It doesn't have to be useful, though.
  • Look at rxmarbles.com it is a great way to visualise the rx functions and helped me greatly when learning rxjs.
  • @adrianbrand did you linked proper link? there are few diagrams and no explanation at all :(
  • The marbles are dragable so you can visualise the streams