source: trip-planner-front/node_modules/rxjs/internal/observable/iif.d.ts@ ceaed42

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1import { Observable } from '../Observable';
2import { SubscribableOrPromise } from '../types';
3/**
4 * Decides at subscription time which Observable will actually be subscribed.
5 *
6 * <span class="informal">`If` statement for Observables.</span>
7 *
8 * `iif` accepts a condition function and two Observables. When
9 * an Observable returned by the operator is subscribed, condition function will be called.
10 * Based on what boolean it returns at that moment, consumer will subscribe either to
11 * the first Observable (if condition was true) or to the second (if condition was false). Condition
12 * function may also not return anything - in that case condition will be evaluated as false and
13 * second Observable will be subscribed.
14 *
15 * Note that Observables for both cases (true and false) are optional. If condition points to an Observable that
16 * was left undefined, resulting stream will simply complete immediately. That allows you to, rather
17 * than controlling which Observable will be subscribed, decide at runtime if consumer should have access
18 * to given Observable or not.
19 *
20 * If you have more complex logic that requires decision between more than two Observables, {@link defer}
21 * will probably be a better choice. Actually `iif` can be easily implemented with {@link defer}
22 * and exists only for convenience and readability reasons.
23 *
24 *
25 * ## Examples
26 * ### Change at runtime which Observable will be subscribed
27 * ```ts
28 * import { iif, of } from 'rxjs';
29 *
30 * let subscribeToFirst;
31 * const firstOrSecond = iif(
32 * () => subscribeToFirst,
33 * of('first'),
34 * of('second'),
35 * );
36 *
37 * subscribeToFirst = true;
38 * firstOrSecond.subscribe(value => console.log(value));
39 *
40 * // Logs:
41 * // "first"
42 *
43 * subscribeToFirst = false;
44 * firstOrSecond.subscribe(value => console.log(value));
45 *
46 * // Logs:
47 * // "second"
48 *
49 * ```
50 *
51 * ### Control an access to an Observable
52 * ```ts
53 * let accessGranted;
54 * const observableIfYouHaveAccess = iif(
55 * () => accessGranted,
56 * of('It seems you have an access...'), // Note that only one Observable is passed to the operator.
57 * );
58 *
59 * accessGranted = true;
60 * observableIfYouHaveAccess.subscribe(
61 * value => console.log(value),
62 * err => {},
63 * () => console.log('The end'),
64 * );
65 *
66 * // Logs:
67 * // "It seems you have an access..."
68 * // "The end"
69 *
70 * accessGranted = false;
71 * observableIfYouHaveAccess.subscribe(
72 * value => console.log(value),
73 * err => {},
74 * () => console.log('The end'),
75 * );
76 *
77 * // Logs:
78 * // "The end"
79 * ```
80 *
81 * @see {@link defer}
82 *
83 * @param {function(): boolean} condition Condition which Observable should be chosen.
84 * @param {Observable} [trueObservable] An Observable that will be subscribed if condition is true.
85 * @param {Observable} [falseObservable] An Observable that will be subscribed if condition is false.
86 * @return {Observable} Either first or second Observable, depending on condition.
87 * @static true
88 * @name iif
89 * @owner Observable
90*/
91export declare function iif<T = never, F = never>(condition: () => boolean, trueResult?: SubscribableOrPromise<T>, falseResult?: SubscribableOrPromise<F>): Observable<T | F>;
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