Error behavior example

src/useBehavior.test.tsx

@@ -0,0 +1,111 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { render } from "@testing-library/react";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { catchError, of, tap, Subject, map } from "rxjs";
+
+import { type Behavior } from "./state/Behavior";
+import { useBehavior } from "./useBehavior";
+import { ObservableScope } from "./state/ObservableScope";
+
+function TestComponent({
+  behavior$,
+  shouldThrow = false,
+  children,
+}: {
+  behavior$: Behavior<string>;
+  shouldThrow?: boolean;
+  children: React.ReactNode;
+}): React.ReactNode {
+  if (shouldThrow) throw Error("Test error");
+
+  const value = useBehavior(behavior$);
+
+  return (
+    <div>
+      value: {value}
+      {children}
+    </div>
+  );
+}
+
+describe("useBehavior", () => {
+  let scope: ObservableScope;
+  beforeEach(() => (scope = new ObservableScope()));
+  afterEach(() => scope.end());
+
+  it("reference test", () => {
+    expect(() =>
+      render(
+        <TestComponent behavior$={scope.behavior(of("test"))}>
+          Test
+        </TestComponent>,
+      ),
+    ).not.toThrow();
+  });
+  it("should return the correct behavior", () => {
+    expect(() =>
+      render(
+        <TestComponent
+          shouldThrow={true}
+          behavior$={scope.behavior(of("test"))}
+        >
+          Test
+        </TestComponent>,
+      ),
+    ).toThrow("Test error");
+  });
+
+  it("useBehavior forwards the throw in obs computation", () => {
+    const throwingOperation = (): string => {
+      throw new Error("Test error");
+      return "a";
+    };
+
+    expect(() => {
+      const s$ = new Subject<string>();
+      const b$ = scope.behavior(s$, "");
+      s$.next("test");
+      s$.next(throwingOperation());
+      render(<TestComponent behavior$={b$}>Test</TestComponent>);
+    }).toThrow("Test error");
+  });
+  it("useBehavior does not throw in caught obs computation", () => {
+    function errorOnE(s: string): string {
+      if (s === "E") throw new Error("Test error");
+      return s + "CheckedForE";
+    }
+
+    console.log("hello");
+    const s$ = new Subject<string>();
+    const b$ = scope.behavior(s$.pipe(map(errorOnE)), "START");
+
+    const inheritForThrowCatch$ = scope.behavior(
+      b$.pipe(
+        tap((v) => console.log("tap-" + v)),
+        catchError((err) => {
+          console.log("caught error" + err);
+          return of("I caught an error and converted it to sth nicer");
+        }),
+      ),
+    );
+
+    s$.next("test");
+    s$.next("E");
+    s$.next("after error");
+
+    expect(() => {
+      render(
+        <TestComponent behavior$={inheritForThrowCatch$}>Test</TestComponent>,
+      );
+    }).not.toThrow();
+    expect(() => {
+      render(<TestComponent behavior$={b$}>Test</TestComponent>);
+    }).toThrow();
+  });
+});

src/useBehavior.ts

@@ -15,7 +15,12 @@ import { type Behavior } from "./state/Behavior";
 export function useBehavior<T>(behavior: Behavior<T>): T {
   const subscribe = useCallback(
     (onChange: () => void) => {
-      const s = behavior.subscribe(onChange);
+      const s = behavior.subscribe({
+        next: onChange,
+        error: (e) => {
+          throw e;
+        },
+      });
       return (): void => s.unsubscribe();
     },
     [behavior],