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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