rxjs
Version:
Reactive Extensions for modern JavaScript
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text/typescript
import { Operator } from '../Operator';
import { Observable, ObservableInput } from '../Observable';
import { Subscriber } from '../Subscriber';
import { Subscription } from '../Subscription';
import { OuterSubscriber } from '../OuterSubscriber';
import { InnerSubscriber } from '../InnerSubscriber';
import { subscribeToResult } from '../util/subscribeToResult';
import { OperatorFunction } from '../interfaces';
/* tslint:disable:max-line-length */
export function switchMapTo<T, R>(observable: ObservableInput<R>): OperatorFunction<T, R>;
export function switchMapTo<T, I, R>(observable: ObservableInput<I>, resultSelector: (outerValue: T, innerValue: I, outerIndex: number, innerIndex: number) => R): OperatorFunction<T, R>;
/* tslint:enable:max-line-length */
/**
* Projects each source value to the same Observable which is flattened multiple
* times with {@link switch} in the output Observable.
*
* <span class="informal">It's like {@link switchMap}, but maps each value
* always to the same inner Observable.</span>
*
* <img src="./img/switchMapTo.png" width="100%">
*
* Maps each source value to the given Observable `innerObservable` regardless
* of the source value, and then flattens those resulting Observables into one
* single Observable, which is the output Observable. The output Observables
* emits values only from the most recently emitted instance of
* `innerObservable`.
*
* @example <caption>Rerun an interval Observable on every click event</caption>
* var clicks = Rx.Observable.fromEvent(document, 'click');
* var result = clicks.switchMapTo(Rx.Observable.interval(1000));
* result.subscribe(x => console.log(x));
*
* @see {@link concatMapTo}
* @see {@link switch}
* @see {@link switchMap}
* @see {@link mergeMapTo}
*
* @param {ObservableInput} innerObservable An Observable to replace each value from
* the source Observable.
* @param {function(outerValue: T, innerValue: I, outerIndex: number, innerIndex: number): any} [resultSelector]
* A function to produce the value on the output Observable based on the values
* and the indices of the source (outer) emission and the inner Observable
* emission. The arguments passed to this function are:
* - `outerValue`: the value that came from the source
* - `innerValue`: the value that came from the projected Observable
* - `outerIndex`: the "index" of the value that came from the source
* - `innerIndex`: the "index" of the value from the projected Observable
* @return {Observable} An Observable that emits items from the given
* `innerObservable` (and optionally transformed through `resultSelector`) every
* time a value is emitted on the source Observable, and taking only the values
* from the most recently projected inner Observable.
* @method switchMapTo
* @owner Observable
*/
export function switchMapTo<T, I, R>(innerObservable: Observable<I>,
resultSelector?: (outerValue: T,
innerValue: I,
outerIndex: number,
innerIndex: number) => R): OperatorFunction<T, I | R> {
return (source: Observable<T>) => source.lift(new SwitchMapToOperator(innerObservable, resultSelector));
}
class SwitchMapToOperator<T, I, R> implements Operator<T, I> {
constructor(private observable: Observable<I>,
private resultSelector?: (outerValue: T, innerValue: I, outerIndex: number, innerIndex: number) => R) {
}
call(subscriber: Subscriber<I>, source: any): any {
return source.subscribe(new SwitchMapToSubscriber(subscriber, this.observable, this.resultSelector));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
class SwitchMapToSubscriber<T, I, R> extends OuterSubscriber<T, I> {
private index: number = 0;
private innerSubscription: Subscription;
constructor(destination: Subscriber<I>,
private inner: Observable<I>,
private resultSelector?: (outerValue: T, innerValue: I, outerIndex: number, innerIndex: number) => R) {
super(destination);
}
protected _next(value: any) {
const innerSubscription = this.innerSubscription;
if (innerSubscription) {
innerSubscription.unsubscribe();
}
this.add(this.innerSubscription = subscribeToResult(this, this.inner, value, this.index++));
}
protected _complete() {
const {innerSubscription} = this;
if (!innerSubscription || innerSubscription.closed) {
super._complete();
}
}
protected _unsubscribe() {
this.innerSubscription = null;
}
notifyComplete(innerSub: Subscription) {
this.remove(innerSub);
this.innerSubscription = null;
if (this.isStopped) {
super._complete();
}
}
notifyNext(outerValue: T, innerValue: I,
outerIndex: number, innerIndex: number,
innerSub: InnerSubscriber<T, I>): void {
const { resultSelector, destination } = this;
if (resultSelector) {
this.tryResultSelector(outerValue, innerValue, outerIndex, innerIndex);
} else {
destination.next(innerValue);
}
}
private tryResultSelector(outerValue: T, innerValue: I,
outerIndex: number, innerIndex: number): void {
const { resultSelector, destination } = this;
let result: R;
try {
result = resultSelector(outerValue, innerValue, outerIndex, innerIndex);
} catch (err) {
destination.error(err);
return;
}
destination.next(result);
}
}