fix: observe fallbackInView option updates in InView

packages/react-intersection-observer/src/InView.tsx

@@ -94,7 +94,8 @@ export class InView extends React.Component<
       prevProps.triggerOnce !== this.props.triggerOnce ||
       prevProps.skip !== this.props.skip ||
       prevProps.trackVisibility !== this.props.trackVisibility ||
-      prevProps.delay !== this.props.delay
+      prevProps.delay !== this.props.delay ||
+      prevProps.fallbackInView !== this.props.fallbackInView
     ) {
       this.unobserve();
       this.observeNode();

packages/react-intersection-observer/src/__tests__/InView.test.tsx

@@ -301,6 +301,30 @@ test("should render with fallback", () => {
   }).toThrow();
 });
 
+test("should update fallbackInView when the observer is unsupported", () => {
+  // @ts-expect-error Simulate a browser without IntersectionObserver.
+  window.IntersectionObserver = undefined;
+  const callback = vi.fn();
+  const { rerender } = render(
+    <InView fallbackInView={true} onChange={callback}>
+      {({ inView, ref }) => <div ref={ref}>{inView.toString()}</div>}
+    </InView>,
+  );
+  screen.getByText("true");
+
+  rerender(
+    <InView fallbackInView={false} onChange={callback}>
+      {({ inView, ref }) => <div ref={ref}>{inView.toString()}</div>}
+    </InView>,
+  );
+
+  screen.getByText("false");
+  expect(callback).toHaveBeenLastCalledWith(
+    false,
+    expect.objectContaining({ isIntersecting: false }),
+  );
+});
+
 test("should render with global fallback", () => {
   const cb = vi.fn();
   // @ts-expect-error