feat: Add OperatorSubscriber.

source/OperatorSubscriber.ts

@@ -0,0 +1,68 @@
+/**
+ * @license Use of this source code is governed by an MIT-style license that
+ * can be found in the LICENSE file at https://github.com/cartant/rxjs-etc
+ */
+
+import { Subscriber } from "rxjs";
+
+export class OperatorSubscriber<
+  TSource,
+  TDestination = TSource
+> extends Subscriber<TSource> {
+  constructor(
+    destination: Subscriber<TSource>,
+    handlers: {
+      next?: undefined;
+      error?: (error: unknown) => void;
+      complete?: () => void;
+    }
+  );
+  constructor(
+    destination: Subscriber<TDestination>,
+    handlers: {
+      next: (value: TSource) => void;
+      error?: (error: unknown) => void;
+      complete?: () => void;
+    }
+  );
+  constructor(
+    destination: Subscriber<TSource | TDestination>,
+    handlers: {
+      next?: (value: TSource) => void;
+      error?: (error: unknown) => void;
+      complete?: () => void;
+    }
+  ) {
+    super(destination);
+    const { complete, error, next } = handlers;
+    if (complete) {
+      this._complete = () => {
+        try {
+          complete();
+        } catch (caught: unknown) {
+          destination.error(caught);
+        }
+        this.unsubscribe();
+      };
+    }
+    if (error) {
+      this._error = (received) => {
+        try {
+          error(received);
+        } catch (caught: unknown) {
+          destination.error(caught);
+        }
+        this.unsubscribe();
+      };
+    }
+    if (next) {
+      this._next = (value: TSource) => {
+        try {
+          next(value);
+        } catch (caught: unknown) {
+          destination.error(caught);
+        }
+      };
+    }
+  }
+}