@acutmore/rxjs/dist/package/internal/observable/IfObservable.d.ts

Reactive Extensions for modern JavaScript

import { Observable, SubscribableOrPromise } from '../Observable';
import { Subscriber } from '../Subscriber';
import { TeardownLogic } from '../Subscription';
/**
 * We need this JSDoc comment for affecting ESDoc.
 * @extends {Ignored}
 * @hide true
 */
export declare class IfObservable<T, R> extends Observable<T> {
    private condition;
    private thenSource;
    private elseSource;
    /**
     * Decides at subscription time which Observable will actually be subscribed.
     *
     * <span class="informal">`If` statement for Observables.</span>
     *
     * `if` accepts a condition function and two Observables. When
     * an Observable returned by the operator is subscribed, condition function will be called.
     * Based on what boolean it returns at that moment, consumer will subscribe either to
     * the first Observable (if condition was true) or to the second (if condition was false). Condition
     * function may also not return anything - in that case condition will be evaluated as false and
     * second Observable will be subscribed.
     *
     * Note that Observables for both cases (true and false) are optional. If condition points to an Observable that
     * was left undefined, resulting stream will simply complete immediately. That allows you to, rather
     * then controlling which Observable will be subscribed, decide at runtime if consumer should have access
     * to given Observable or not.
     *
     * If you have more complex logic that requires decision between more than two Observables, {@link defer}
     * will probably be a better choice. Actually `if` can be easily implemented with {@link defer}
     * and exists only for convenience and readability reasons.
     *
     *
     * @example <caption>Change at runtime which Observable will be subscribed</caption>
     * let subscribeToFirst;
     * const firstOrSecond = Rx.Observable.if(
     *   () => subscribeToFirst,
     *   Rx.Observable.of('first'),
     *   Rx.Observable.of('second')
     * );
     *
     * subscribeToFirst = true;
     * firstOrSecond.subscribe(value => console.log(value));
     *
     * // Logs:
     * // "first"
     *
     * subscribeToFirst = false;
     * firstOrSecond.subscribe(value => console.log(value));
     *
     * // Logs:
     * // "second"
     *
     *
     * @example <caption>Control an access to an Observable</caption>
     * let accessGranted;
     * const observableIfYouHaveAccess = Rx.Observable.if(
     *   () => accessGranted,
     *   Rx.Observable.of('It seems you have an access...') // Note that only one Observable is passed to the operator.
     * );
     *
     * accessGranted = true;
     * observableIfYouHaveAccess.subscribe(
     *   value => console.log(value),
     *   err => {},
     *   () => console.log('The end')
     * );
     *
     * // Logs:
     * // "It seems you have an access..."
     * // "The end"
     *
     * accessGranted = false;
     * observableIfYouHaveAccess.subscribe(
     *   value => console.log(value),
     *   err => {},
     *   () => console.log('The end')
     * );
     *
     * // Logs:
     * // "The end"
     *
     * @see {@link defer}
     *
     * @param {function(): boolean} condition Condition which Observable should be chosen.
     * @param {Observable} [trueObservable] An Observable that will be subscribed if condition is true.
     * @param {Observable} [falseObservable] An Observable that will be subscribed if condition is false.
     * @return {Observable} Either first or second Observable, depending on condition.
     * @static true
     * @name if
     * @owner Observable
     */
    static create<T, R>(condition: () => boolean | void, thenSource?: SubscribableOrPromise<T> | void, elseSource?: SubscribableOrPromise<R> | void): Observable<T | R>;
    constructor(condition: () => boolean | void, thenSource?: SubscribableOrPromise<T> | void, elseSource?: SubscribableOrPromise<R> | void);
    protected _subscribe(subscriber: Subscriber<T | R>): TeardownLogic;
}