Vendorize queueing-subject

src/app/services/queueing-subject.ts

@@ -0,0 +1,26 @@
+// Based on https://github.com/ohjames/queueing-subject
+
+import { Subject, Subscriber, Subscription } from 'rxjs';
+
+export class QueueingSubject<T> extends Subject<T> {
+  private queuedValues: T[] = [];
+
+  next(value: T): void {
+    if (this.closed || this.observers.length) {
+      super.next(value);
+    } else {
+      this.queuedValues.push(value);
+    }
+  }
+
+  _subscribe(subscriber: Subscriber<T>): Subscription {
+    const subscription = super._subscribe(subscriber);
+
+    if (this.queuedValues.length) {
+      this.queuedValues.forEach(value => super.next(value));
+      this.queuedValues.splice(0);
+    }
+
+    return subscription;
+  }
+}