[RxJS] Use RxJS concatMap to map and concat high order observables

Like switchMap and mergeMap, concatMap is a shortcut for map() followed by a concatAll(). In this lesson we will explore this RxJS operator and its properties.

const clickObservable = Rx.Observable

  .fromEvent(document, 'click');

function performRequest() {

  return fetch('https://jsonplaceholder.typicode.com/users/1')

    .then(res => res.json());

}

const emailObservable = clickObservable

  .concatMap(click => performRequest(),

             (click, res) => res.email);

// concatMap = map ... + ... concatAll

// mergeMap

// switchMap

emailObservable

  .subscribe(email => console.log(email));

concatMap happens one after the other, the same as mergeAll(1):

const emailObservable = clickObservable

  .mergeMap(click => performRequest(),

             (click, res) => res.email,

           );

So the main different between switchMap, mergeMap, concatMap are about concurrency...

switchMap: has cancel previous request functionaility.
mergeMap: allows num of concurrency requests
concatMap: the same as mergeAll(1), only allow one request at a time

巴特西

[RxJS] Use RxJS concatMap to map and concat high order observables

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