diff --git a/gitbook/reactjrx/SUMMARY.md b/gitbook/reactjrx/SUMMARY.md
index 8f76371..e6d2c1a 100644
--- a/gitbook/reactjrx/SUMMARY.md
+++ b/gitbook/reactjrx/SUMMARY.md
@@ -43,6 +43,7 @@
 * [React](utils/react/README.md)
   * [useMount](utils/react/usemount.md)
   * [useEffectOnce](utils/react/useeffectonce.md)
+  * [useUnmount](utils/react/useunmount.md)
   * [useConstant](utils/react/useconstant.md)
   * [useLiveRef](utils/react/useliveref.md)
   * [useDebounced](utils/react/usedebounced.md)
diff --git a/gitbook/reactjrx/utils/react/useeffectonce.md b/gitbook/reactjrx/utils/react/useeffectonce.md
index ed59fd7..2a6955c 100644
--- a/gitbook/reactjrx/utils/react/useeffectonce.md
+++ b/gitbook/reactjrx/utils/react/useeffectonce.md
@@ -1,6 +1,10 @@
 # useEffectOnce
 
-React lifecycle hook that runs an effect only once.
+React lifecycle hook that runs an effect once, when the component mounts.
+
+{% hint style="warning" %}
+In development, under `<StrictMode>`, React mounts each component twice. So the effect runs twice, with its cleanup between the two runs. Make the cleanup undo the effect.
+{% endhint %}
 
 ### Usage <a href="#usage" id="usage"></a>
 
diff --git a/gitbook/reactjrx/utils/react/usemount.md b/gitbook/reactjrx/utils/react/usemount.md
index 684e30a..0946aa1 100644
--- a/gitbook/reactjrx/utils/react/usemount.md
+++ b/gitbook/reactjrx/utils/react/usemount.md
@@ -2,6 +2,10 @@
 
 React lifecycle hook that calls a function after the component is mounted.
 
+{% hint style="warning" %}
+In development, under `<StrictMode>`, React mounts each component twice. So `useMount` calls `fn` twice. Make `fn` safe to call twice, or use `useEffectOnce` and undo the work in its cleanup.
+{% endhint %}
+
 ### Usage <a href="#usage" id="usage"></a>
 
 ```jsx
diff --git a/gitbook/reactjrx/utils/react/useunmount.md b/gitbook/reactjrx/utils/react/useunmount.md
new file mode 100644
index 0000000..a24c88a
--- /dev/null
+++ b/gitbook/reactjrx/utils/react/useunmount.md
@@ -0,0 +1,24 @@
+# useUnmount
+
+React lifecycle hook that calls a function when the component unmounts. It calls the `fn` of the last committed render.
+
+{% hint style="warning" %}
+In development, under `<StrictMode>`, React mounts each component twice. So `useUnmount` also calls `fn` once after the first mount, while the component stays mounted. Do not end work there that the component still uses, such as a subject that it reads.
+{% endhint %}
+
+### Usage
+
+```jsx
+import {useUnmount} from 'reactjrx';
+
+const Demo = ({ onClose }) => {
+  useUnmount(() => onClose());
+  return null;
+};
+```
+
+### Reference
+
+```ts
+useUnmount(fn: () => any);
+```
diff --git a/src/lib/utils/react/useUnmount.test.tsx b/src/lib/utils/react/useUnmount.test.tsx
new file mode 100644
index 0000000..58ab3e0
--- /dev/null
+++ b/src/lib/utils/react/useUnmount.test.tsx
@@ -0,0 +1,60 @@
+import { render, renderHook } from "@testing-library/react"
+import { act, Suspense, startTransition, use, useState } from "react"
+import { describe, expect, it, vi } from "vitest"
+import { useUnmount } from "./useUnmount"
+
+describe("useUnmount", () => {
+  it("should call the fn of the last render when the component unmounts", () => {
+    const first = vi.fn()
+    const latest = vi.fn()
+    const { rerender, unmount } = renderHook(({ fn }) => useUnmount(fn), {
+      initialProps: { fn: first },
+    })
+
+    rerender({ fn: latest })
+    unmount()
+
+    expect(first).not.toHaveBeenCalled()
+    expect(latest).toHaveBeenCalledTimes(1)
+  })
+
+  it("should call the committed fn when React drops a render", async () => {
+    const never = new Promise<never>(() => {})
+    const Suspends = () => {
+      "use no memo"
+
+      use(never)
+
+      return null
+    }
+    const committed = vi.fn()
+    const dropped = vi.fn()
+    const rendered: Array<() => void> = []
+    let setFn: (fn: () => void) => void = () => {}
+
+    const Comp = () => {
+      "use no memo"
+
+      const [fn, set] = useState<() => void>(() => committed)
+      setFn = set
+      rendered.push(fn)
+      useUnmount(fn)
+
+      return (
+        <Suspense fallback={null}>{fn === dropped && <Suspends />}</Suspense>
+      )
+    }
+
+    const { unmount } = render(<Comp />)
+
+    await act(async () => {
+      startTransition(() => setFn(() => dropped))
+    })
+
+    unmount()
+
+    expect(rendered).toContain(dropped)
+    expect(dropped).not.toHaveBeenCalled()
+    expect(committed).toHaveBeenCalledTimes(1)
+  })
+})
diff --git a/src/lib/utils/react/useUnmount.ts b/src/lib/utils/react/useUnmount.ts
index 137c5ac..7b10c9c 100644
--- a/src/lib/utils/react/useUnmount.ts
+++ b/src/lib/utils/react/useUnmount.ts
@@ -1,12 +1,9 @@
-import { useRef } from "react"
 import { useEffectOnce } from "./useEffectOnce"
+import { useLiveRef } from "./useLiveRef"
 
 // biome-ignore lint/suspicious/noExplicitAny: Expected any
 export const useUnmount = (fn: () => any): void => {
-  const fnRef = useRef(fn)
-
-  // update the ref each render so if it change the newest callback will be invoked
-  fnRef.current = fn
+  const fnRef = useLiveRef(fn)
 
   useEffectOnce(() => () => fnRef.current())
 }