[Reactive Programming] Async requests and responses in RxJS

We will learn how to perform network requests to a backend using RxJS Observables.

A example of basic jquery request:

console.clear();
var requestStream = Rx.Observable.just('https://api.github.com/users');

//Current requestStream is just a stream 
//We need to subscribe it to make it work
requestStream.subscribe(url => {
  
  //Preform a serve reqest by jQuery
  jQuery.getJSON(url).done( res => {
    console.log(res);
  })
});

But it not make so many sence we use jQuery to handle the promise since we already using RxJS:

console.clear();
var requestStream = Rx.Observable.just('https://api.github.com/users');

//Current requestStream is just a stream 
//We need to subscribe it to make it work
requestStream.subscribe( url => {
  
  //Using Rx.Observable.fromPromise() to handle the response
  //Since jQuery.getJSON(url) return a promise
  //there we put into the fromPromise() function
  var responseStream = Rx.Observable.fromPromise(jQuery.getJSON(url));
  
  //Then subscribe the responseStream 
  responseStream.subscribe( res => {
    console.log(res);
  });
});

We see that we can accomplish with promise we also can do in Observable. And the main problem for promise is that promise only even yield a single value. But observalbe can have mult events.

But soon we find we subscribe an stream inside another subscribe, this is what we don't have to do, normal way to avoid this is using flatMap().

Here we do flagMap() but not map() is because inside map() a observable and return another observable then we got an observable of observable. 

console.clear();
var requestStream = Rx.Observable.just('https://api.github.com/users');
var responseStream = requestStream
  .flatMap( url => Rx.Observable.fromPromise(jQuery.getJSON(url)));

responseStream.subscribe( res => console.log(res));

Now we have only one subscribe.