From aedba6d9950f0deef67e96e03a4aa23b5f76a997 Mon Sep 17 00:00:00 2001
From: Sergey Volkov <js2me@outlook.com>
Date: Fri, 23 Jan 2026 14:38:33 +0300
Subject: [PATCH] feat: optimize withViewModel HOC (remove observer wrapper)

---
 .changeset/tame-lands-drive.md         |  5 ++
 src/react/hoc/with-view-model.test.tsx | 78 +++++++++++++++++++++++++-
 src/react/hoc/with-view-model.tsx      | 45 ++++++++-------
 3 files changed, 105 insertions(+), 23 deletions(-)
 create mode 100644 .changeset/tame-lands-drive.md

diff --git a/.changeset/tame-lands-drive.md b/.changeset/tame-lands-drive.md
new file mode 100644
index 00000000..fa93d516
--- /dev/null
+++ b/.changeset/tame-lands-drive.md
@@ -0,0 +1,5 @@
+---
+"mobx-view-model": minor
+---
+
+optimize `withViewModel` HOC with replaced `observer()` wrap HOC to `<Observer>` component use
diff --git a/src/react/hoc/with-view-model.test.tsx b/src/react/hoc/with-view-model.test.tsx
index 95a20991..b4d47e80 100644
--- a/src/react/hoc/with-view-model.test.tsx
+++ b/src/react/hoc/with-view-model.test.tsx
@@ -109,6 +109,74 @@ describe('withViewModel', () => {
     expect(spyFallbackRender).toHaveBeenCalledTimes(1);
   });
 
+  test('updates UI when isMounted becomes true', async () => {
+    class VM extends ViewModelBaseMock {
+      mount() {
+        setTimeout(() => {
+          super.mount();
+        }, 20);
+      }
+    }
+    const View = ({ model }: ViewModelProps<VM>) => {
+      return <div data-testid={'view'}>{`hello ${model.id}`}</div>;
+    };
+    const Fallback = () => {
+      return <div data-testid={'fallback'}>fallback</div>;
+    };
+    const Component = withViewModel(VM, {
+      generateId: createIdGenerator(),
+      fallback: Fallback,
+    })(View);
+
+    render(<Component />);
+
+    expect(screen.getByTestId('fallback')).toBeDefined();
+
+    await act(async () => {
+      await sleep(30);
+    });
+
+    expect(screen.getByTestId('view')).toBeDefined();
+  });
+
+  test('updates UI when isMounted becomes false', async () => {
+    class VM extends ViewModelBaseMock {
+      triggerUnmount() {
+        this.unmount();
+      }
+    }
+    const View = ({ model }: ViewModelProps<VM>) => {
+      return (
+        <div>
+          <button
+            data-testid={'unmount'}
+            onClick={() => model.triggerUnmount()}
+          >
+            unmount
+          </button>
+          <div data-testid={'view'}>{`hello ${model.id}`}</div>
+        </div>
+      );
+    };
+    const Fallback = () => {
+      return <div data-testid={'fallback'}>fallback</div>;
+    };
+    const Component = withViewModel(VM, {
+      generateId: createIdGenerator(),
+      fallback: Fallback,
+    })(View);
+
+    await act(async () => render(<Component />));
+
+    expect(screen.getByTestId('view')).toBeDefined();
+
+    await act(async () => {
+      fireEvent.click(screen.getByTestId('unmount'));
+    });
+
+    expect(screen.getByTestId('fallback')).toBeDefined();
+  });
+
   test('renders fallback before render REAL COMPONENT (times)', async () => {
     class VM extends ViewModelBaseMock {}
     const View = ({ model }: ViewModelProps<VM>) => {
@@ -249,7 +317,7 @@ describe('withViewModel', () => {
     expect(screen.getByText('second-VM_1')).toBeDefined();
   });
 
-  test('withViewModel wrapper should by only mounted (renders 2 times)', () => {
+  test('withViewModel wrapper should by only mounted (renders 1 time)', () => {
     class VM extends ViewModelBaseMock {}
     const View = vi.fn(({ model }: ViewModelProps<VM>) => {
       return <div>{`hello ${model.id}`}</div>;
@@ -263,7 +331,7 @@ describe('withViewModel', () => {
     })(View);
 
     render(<Component />);
-    expect(useHookSpy).toHaveBeenCalledTimes(2);
+    expect(useHookSpy).toHaveBeenCalledTimes(1);
   });
 
   describe('payload manipulations', () => {
@@ -746,7 +814,11 @@ describe('withViewModel', () => {
 
       await sleep(200);
 
-      expect(setPayloadSpy).toHaveBeenCalledTimes(2);
+      expect(setPayloadSpy).toHaveBeenCalledTimes(1);
+      expect(setPayloadSpy.mock.calls[0]?.[0]).toMatchObject({
+        techreviewId: '1',
+        selectedCompIds: ['1', '2', '3'],
+      });
     });
   });
 
diff --git a/src/react/hoc/with-view-model.tsx b/src/react/hoc/with-view-model.tsx
index a64a69bf..b4435337 100644
--- a/src/react/hoc/with-view-model.tsx
+++ b/src/react/hoc/with-view-model.tsx
@@ -1,4 +1,4 @@
-import { observer } from 'mobx-react-lite';
+import { Observer, observer } from 'mobx-react-lite';
 import { forwardRef, useContext } from 'react';
 import type {
   AnyObject,
@@ -373,24 +373,31 @@ const withViewModelWrapper = (
       props: componentProps,
     }) as unknown as AnyViewModel | AnyViewModelSimple;
 
-    const isRenderAllowedByStore =
-      !viewModels || viewModels.isAbleToRenderView(model.id);
-
-    // This condition is works for AnyViewModelSimple too
-    // All other variants will be bad for performance
-    const isRenderAllowed =
-      isRenderAllowedByStore && (model as AnyViewModel).isMounted !== false;
-
-    if (isRenderAllowed) {
-      return (
-        <ActiveViewModelProvider value={model}>
-          {Component && <Component {...componentProps} model={model} />}
-        </ActiveViewModelProvider>
-      );
-    }
-
     return (
-      FallbackComponent && <FallbackComponent {...allProps} payload={payload} />
+      <Observer>
+        {() => {
+          const isRenderAllowedByStore =
+            !viewModels || viewModels.isAbleToRenderView(model.id);
+
+          // This condition is works for AnyViewModelSimple too
+          // All other variants will be bad for performance
+          const isRenderAllowed =
+            isRenderAllowedByStore &&
+            (model as AnyViewModel).isMounted !== false;
+
+          if (isRenderAllowed) {
+            return (
+              <ActiveViewModelProvider value={model}>
+                {Component && <Component {...componentProps} model={model} />}
+              </ActiveViewModelProvider>
+            );
+          }
+
+          return FallbackComponent ? (
+            <FallbackComponent {...allProps} payload={payload} />
+          ) : null;
+        }}
+      </Observer>
     );
   };
 
@@ -400,8 +407,6 @@ const withViewModelWrapper = (
     ConnectedViewModel = forwardRef(ConnectedViewModel) as any;
   }
 
-  ConnectedViewModel = observer(ConnectedViewModel);
-
   if (process.env.NODE_ENV !== 'production') {
     (ConnectedViewModel as React.ComponentType).displayName =
       `ConnectedViewModel(${VM.name}->Component)`;