es6/operator/switchMapTo.js

import { OuterSubscriber } from '../OuterSubscriber';
import { subscribeToResult } from '../util/subscribeToResult';
/* tslint:enable:max-line-length */
/**
 * 将每个源值投射成同一个 Observable ，该 Observable 会使用 {@link switch} 多次被打平
 * 到输出 Observable 中。
 *
 * <span class="informal">它很像 {@link switchMap}，但永远将每个值映射到同一个内部
 + * Observable 。</span>
 *
 * <img src="./img/switchMapTo.png" width="100%">
 *
 * 将每个源值映射成给定的 Observable ：`innerObservable` ，而无论源值是什么，然后
 * 将这些结果 Observables 合并到单个的 Observable ，也就是输出 Observable 。
 * 输出 Observables 只会发出 `innerObservable` 实例最新发出的值。
 *
 * @example <caption>每次点击返回一个 interval Observable</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 用来替换源 Observable 中的每个值
 * 的 Observable 。
 * @param {function(outerValue: T, innerValue: I, outerIndex: number, innerIndex: number): any} [resultSelector]
 * 函数，它用于产生基于值的输出 Observable 和源(外部)发送和内部 Observable 发送的索引。
 * 传递给这个函数参数有：
 * - `outerValue`: 来自源的值
 * - `innerValue`: 来自投射的 Observable 的值
 * - `outerIndex`: 来自源的值的 "index"
 * - `innerIndex`: 来自投射的 Observable 的值的 "index"
 * @return {Observable} 每次源 Observable 发出值时，该 Observable 发出来自
 * 给定 `innerObservable` (和通过 `resultSelector` 的可选的转换)的项，
 * 并只接收最新投射的内部 Observable 的值。
 * @method switchMapTo
 * @owner Observable
 */
export function switchMapTo(innerObservable, resultSelector) {
    return this.lift(new SwitchMapToOperator(innerObservable, resultSelector));
}
class SwitchMapToOperator {
    constructor(observable, resultSelector) {
        this.observable = observable;
        this.resultSelector = resultSelector;
    }
    call(subscriber, source) {
        return source.subscribe(new SwitchMapToSubscriber(subscriber, this.observable, this.resultSelector));
    }
}
/**
 * We need this JSDoc comment for affecting ESDoc.
 * @ignore
 * @extends {Ignored}
 */
class SwitchMapToSubscriber extends OuterSubscriber {
    constructor(destination, inner, resultSelector) {
        super(destination);
        this.inner = inner;
        this.resultSelector = resultSelector;
        this.index = 0;
    }
    _next(value) {
        const innerSubscription = this.innerSubscription;
        if (innerSubscription) {
            innerSubscription.unsubscribe();
        }
        this.add(this.innerSubscription = subscribeToResult(this, this.inner, value, this.index++));
    }
    _complete() {
        const { innerSubscription } = this;
        if (!innerSubscription || innerSubscription.closed) {
            super._complete();
        }
    }
    _unsubscribe() {
        this.innerSubscription = null;
    }
    notifyComplete(innerSub) {
        this.remove(innerSub);
        this.innerSubscription = null;
        if (this.isStopped) {
            super._complete();
        }
    }
    notifyNext(outerValue, innerValue, outerIndex, innerIndex, innerSub) {
        const { resultSelector, destination } = this;
        if (resultSelector) {
            this.tryResultSelector(outerValue, innerValue, outerIndex, innerIndex);
        }
        else {
            destination.next(innerValue);
        }
    }
    tryResultSelector(outerValue, innerValue, outerIndex, innerIndex) {
        const { resultSelector, destination } = this;
        let result;
        try {
            result = resultSelector(outerValue, innerValue, outerIndex, innerIndex);
        }
        catch (err) {
            destination.error(err);
            return;
        }
        destination.next(result);
    }
}
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