[6a3a178] | 1 | import { Operator } from '../Operator';
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| 2 | import { Subscriber } from '../Subscriber';
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| 3 | import { Observable } from '../Observable';
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| 4 | import { OperatorFunction } from '../types';
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| 5 |
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| 6 | /**
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| 7 | * Emits false if the input observable emits any values, or emits true if the
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| 8 | * input observable completes without emitting any values.
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| 9 | *
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| 10 | * <span class="informal">Tells whether any values are emitted by an observable</span>
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| 11 | *
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| 12 | * ![](isEmpty.png)
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| 13 | *
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| 14 | * `isEmpty` transforms an Observable that emits values into an Observable that
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| 15 | * emits a single boolean value representing whether or not any values were
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| 16 | * emitted by the source Observable. As soon as the source Observable emits a
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| 17 | * value, `isEmpty` will emit a `false` and complete. If the source Observable
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| 18 | * completes having not emitted anything, `isEmpty` will emit a `true` and
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| 19 | * complete.
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| 20 | *
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| 21 | * A similar effect could be achieved with {@link count}, but `isEmpty` can emit
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| 22 | * a `false` value sooner.
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| 23 | *
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| 24 | * ## Examples
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| 25 | *
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| 26 | * Emit `false` for a non-empty Observable
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| 27 | * ```javascript
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| 28 | * import { Subject } from 'rxjs';
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| 29 | * import { isEmpty } from 'rxjs/operators';
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| 30 | *
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| 31 | * const source = new Subject<string>();
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| 32 | * const result = source.pipe(isEmpty());
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| 33 | * source.subscribe(x => console.log(x));
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| 34 | * result.subscribe(x => console.log(x));
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| 35 | * source.next('a');
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| 36 | * source.next('b');
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| 37 | * source.next('c');
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| 38 | * source.complete();
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| 39 | *
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| 40 | * // Results in:
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| 41 | * // a
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| 42 | * // false
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| 43 | * // b
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| 44 | * // c
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| 45 | * ```
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| 46 | *
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| 47 | * Emit `true` for an empty Observable
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| 48 | * ```javascript
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| 49 | * import { EMPTY } from 'rxjs';
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| 50 | * import { isEmpty } from 'rxjs/operators';
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| 51 | *
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| 52 | * const result = EMPTY.pipe(isEmpty());
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| 53 | * result.subscribe(x => console.log(x));
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| 54 | * // Results in:
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| 55 | * // true
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| 56 | * ```
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| 57 | *
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| 58 | * @see {@link count}
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| 59 | * @see {@link EMPTY}
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| 60 | *
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| 61 | * @return {OperatorFunction<T, boolean>} An Observable of a boolean value indicating whether observable was empty or not
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| 62 | * @method isEmpty
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| 63 | * @owner Observable
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| 64 | */
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| 65 |
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| 66 | export function isEmpty<T>(): OperatorFunction<T, boolean> {
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| 67 | return (source: Observable<T>) => source.lift(new IsEmptyOperator());
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| 68 | }
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| 69 |
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| 70 | class IsEmptyOperator implements Operator<any, boolean> {
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| 71 | call (observer: Subscriber<boolean>, source: any): any {
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| 72 | return source.subscribe(new IsEmptySubscriber(observer));
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| 73 | }
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| 74 | }
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| 75 |
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| 76 | /**
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| 77 | * We need this JSDoc comment for affecting ESDoc.
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| 78 | * @ignore
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| 79 | * @extends {Ignored}
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| 80 | */
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| 81 | class IsEmptySubscriber extends Subscriber<any> {
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| 82 | constructor(destination: Subscriber<boolean>) {
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| 83 | super(destination);
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| 84 | }
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| 85 |
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| 86 | private notifyComplete(isEmpty: boolean): void {
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| 87 | const destination = this.destination;
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| 88 |
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| 89 | destination.next(isEmpty);
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| 90 | destination.complete();
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| 91 | }
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| 92 |
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| 93 | protected _next(value: boolean) {
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| 94 | this.notifyComplete(false);
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| 95 | }
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| 96 |
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| 97 | protected _complete() {
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| 98 | this.notifyComplete(true);
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| 99 | }
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| 100 | }
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