operators/flatMap.js

  1. import { Observable } from '../Observable';
  2. import { passThroughNextObservable } from './passThroughNextObservable';
  3. import { onSubscriptionsComplete } from '../utilities/onSubscriptionsComplete';
  5. /**
  6.  * Same as `map(obs$, mapCallback)` but will take the value of the callback and turn it from an observable to a value
  7.  * 
  8.  * @memberof operators
  9.  *
  10.  * @param {Observable} source$
  11.  * @param {Function} mapCallback
  12.  * @returns {Observable}
  13.  */
  14. export const flatMap = function (source$, mapCallback) {
  15.   return new Observable((observer) => {
  16.     let subscription = { isComplete: false };
  17.     const nextSubscriptionList = [];
  18.     const onComplete = () => onSubscriptionsComplete(
  19.       [subscription, ...nextSubscriptionList],
  20.       observer.complete
  21.     );
  22.     
  23.     subscription = passThroughNextObservable(source$, mapCallback)
  24.       .subscribe((nextValue$) => {
  25.         const nextSubscription = nextValue$.subscribe(
  26.           observer.next,
  27.           observer.error,
  28.           onComplete
  29.         );
  30.         
  31.         nextSubscriptionList.push(nextSubscription);
  32.       }, observer.error, onComplete);
  33.     
  34.     return () => {
  35.       nextSubscriptionList.forEach((nextSub) => nextSub.unsubscribe());
  36.       subscription.unsubscribe();
  37.     };
  38.   });
  39. };
  41. Observable.flatMap = flatMap;
  42. Observable.prototype.flatMap = function (mapCallback) {
  43.   return flatMap(this, mapCallback);
  44. };