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1 | import { Observable } from '../Observable';
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2 | import { noop } from '../util/noop';
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3 |
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4 | /**
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5 | * An Observable that emits no items to the Observer and never completes.
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6 | *
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7 | * ![](never.png)
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8 | *
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9 | * A simple Observable that emits neither values nor errors nor the completion
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10 | * notification. It can be used for testing purposes or for composing with other
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11 | * Observables. Please note that by never emitting a complete notification, this
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12 | * Observable keeps the subscription from being disposed automatically.
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13 | * Subscriptions need to be manually disposed.
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14 | *
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15 | * ## Example
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16 | * ### Emit the number 7, then never emit anything else (not even complete)
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17 | * ```ts
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18 | * import { NEVER } from 'rxjs';
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19 | * import { startWith } from 'rxjs/operators';
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20 | *
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21 | * function info() {
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22 | * console.log('Will not be called');
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23 | * }
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24 | * const result = NEVER.pipe(startWith(7));
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25 | * result.subscribe(x => console.log(x), info, info);
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26 | *
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27 | * ```
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28 | *
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29 | * @see {@link Observable}
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30 | * @see {@link index/EMPTY}
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31 | * @see {@link of}
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32 | * @see {@link throwError}
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33 | */
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34 | export const NEVER = new Observable<never>(noop);
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35 |
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36 | /**
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37 | * @deprecated Deprecated in favor of using {@link NEVER} constant.
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38 | */
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39 | export function never () {
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40 | return NEVER;
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41 | }
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