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node_modules/rxjs/src/internal/operators/defaultIfEmpty.ts

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+import { Operator } from '../Operator';
+import { Observable } from '../Observable';
+import { Subscriber } from '../Subscriber';
+import { OperatorFunction, MonoTypeOperatorFunction } from '../types';
+
+/* tslint:disable:max-line-length */
+export function defaultIfEmpty<T>(defaultValue?: T): MonoTypeOperatorFunction<T>;
+export function defaultIfEmpty<T, R>(defaultValue?: R): OperatorFunction<T, T | R>;
+/* tslint:enable:max-line-length */
+
+/**
+ * Emits a given value if the source Observable completes without emitting any
+ * `next` value, otherwise mirrors the source Observable.
+ *
+ * <span class="informal">If the source Observable turns out to be empty, then
+ * this operator will emit a default value.</span>
+ *
+ * ![](defaultIfEmpty.png)
+ *
+ * `defaultIfEmpty` emits the values emitted by the source Observable or a
+ * specified default value if the source Observable is empty (completes without
+ * having emitted any `next` value).
+ *
+ * ## Example
+ * If no clicks happen in 5 seconds, then emit "no clicks"
+ * ```ts
+ * import { fromEvent } from 'rxjs';
+ * import { defaultIfEmpty, takeUntil } from 'rxjs/operators';
+ *
+ * const clicks = fromEvent(document, 'click');
+ * const clicksBeforeFive = clicks.pipe(takeUntil(interval(5000)));
+ * const result = clicksBeforeFive.pipe(defaultIfEmpty('no clicks'));
+ * result.subscribe(x => console.log(x));
+ * ```
+ *
+ * @see {@link empty}
+ * @see {@link last}
+ *
+ * @param {any} [defaultValue=null] The default value used if the source
+ * Observable is empty.
+ * @return {Observable} An Observable that emits either the specified
+ * `defaultValue` if the source Observable emits no items, or the values emitted
+ * by the source Observable.
+ * @method defaultIfEmpty
+ * @owner Observable
+ */
+export function defaultIfEmpty<T, R>(defaultValue: R = null): OperatorFunction<T, T | R> {
+  return (source: Observable<T>) => source.lift(new DefaultIfEmptyOperator(defaultValue)) as Observable<T | R>;
+}
+
+class DefaultIfEmptyOperator<T, R> implements Operator<T, T | R> {
+
+  constructor(private defaultValue: R) {
+  }
+
+  call(subscriber: Subscriber<T | R>, source: any): any {
+    return source.subscribe(new DefaultIfEmptySubscriber(subscriber, this.defaultValue));
+  }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+class DefaultIfEmptySubscriber<T, R> extends Subscriber<T> {
+  private isEmpty: boolean = true;
+
+  constructor(destination: Subscriber<T | R>, private defaultValue: R) {
+    super(destination);
+  }
+
+  protected _next(value: T): void {
+    this.isEmpty = false;
+    this.destination.next(value);
+  }
+
+  protected _complete(): void {
+    if (this.isEmpty) {
+      this.destination.next(this.defaultValue);
+    }
+    this.destination.complete();
+  }
+}