import { Observable } from '../Observable';
|
import { SubscribableOrPromise } from '../types';
|
/**
|
* Decides at subscription time which Observable will actually be subscribed.
|
*
|
* <span class="informal">`If` statement for Observables.</span>
|
*
|
* `iif` 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
|
* than 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 `iif` can be easily implemented with {@link defer}
|
* and exists only for convenience and readability reasons.
|
*
|
*
|
* ## Examples
|
* ### Change at runtime which Observable will be subscribed
|
* ```ts
|
* import { iif, of } from 'rxjs';
|
*
|
* let subscribeToFirst;
|
* const firstOrSecond = iif(
|
* () => subscribeToFirst,
|
* of('first'),
|
* of('second'),
|
* );
|
*
|
* subscribeToFirst = true;
|
* firstOrSecond.subscribe(value => console.log(value));
|
*
|
* // Logs:
|
* // "first"
|
*
|
* subscribeToFirst = false;
|
* firstOrSecond.subscribe(value => console.log(value));
|
*
|
* // Logs:
|
* // "second"
|
*
|
* ```
|
*
|
* ### Control an access to an Observable
|
* ```ts
|
* let accessGranted;
|
* const observableIfYouHaveAccess = iif(
|
* () => accessGranted,
|
* 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 iif
|
* @owner Observable
|
*/
|
export declare function iif<T = never, F = never>(condition: () => boolean, trueResult?: SubscribableOrPromise<T>, falseResult?: SubscribableOrPromise<F>): Observable<T | F>;
|
