message: docs(operators): Added docs/examples for isEmpty
diff: @@ -3,6 +3,66 @@ import { Subscriber } from '../Subscriber';
  import { Observable } from '../Observable';
  import { OperatorFunction } from '../types';
  +/**
  + * Emits false if the input observable emits any values, or emits true if the
  + * input observable completes without emitting any values.
  + *
  + * <span class="informal">Tells whether any values are emitted by an observable</span>
  + *
  + * ![](isEmpty.png)
  + *
  + * `isEmpty` transforms an Observable that emits values into an Observable that
  + * emits a single boolean value representing whether or not any values were
  + * emitted by the source Observable. As soon as the source Observable emits a
  + * value, `isEmpty` will emit a `false` and complete. If the source Observable
  + * completes having not emitted anything, `isEmpty` will emit a `true` and
  + * complete.
  + *
  + * A similar effect could be achieved with {@link count}, but `isEmpty` can emit
  + * a `false` value sooner.
  + *
  + * ## Examples
  + *
  + * Emit `false` for a non-empty Observable
  + * ```javascript
  + * import { Subject } from 'rxjs';
  + * import { isEmpty } from 'rxjs/operators';
  + *
  + * const source = new Subject<string>();
  + * const result = source.pipe(isEmpty());
  + * source.subscribe(x => console.log(x));
  + * result.subscribe(x => console.log(x));
  + * source.next('a');
  + * source.next('b');
  + * source.next('c');
  + * source.complete();
  + *
  + * // Results in:
  + * // a
  + * // false
  + * // b
  + * // c
  + * ```
  + *
  + * Emit `true` for an empty Observable
  + * ```javascript
  + * import { EMPTY } from 'rxjs';
  + * import { isEmpty } from 'rxjs/operators';
  + *
  + * const result = EMPTY.pipe(isEmpty());
  + * result.subscribe(x => console.log(x));
  + * // Results in:
  + * // true
  + * ```
  + *
  + * @see {@link count}
  + * @see {@link EMPTY}
  + *
  + * @return {OperatorFunction<T, boolean>} An Observable of a boolean value indicating whether observable was empty or not
  + * @method isEmpty
  + * @owner Observable
  + */
  +
  export function isEmpty<T>(): OperatorFunction<T, boolean> {
  return (source: Observable<T>) => source.lift(new IsEmptyOperator());
  }
  