fix(BackTop): should hide when deactivated (#11938)

* fix(site): don't cache components using teleport

* feat: adapt keep-alive

packages/vant/src/back-top/BackTop.tsx

@@ -9,6 +9,8 @@ import {
   type PropType,
   type TeleportProps,
   type ExtractPropTypes,
+  onDeactivated,
+  onActivated,
 } from 'vue';
 
 // Utils
@@ -57,6 +59,7 @@ export default defineComponent({
   emits: ['click'],
 
   setup(props, { emit, slots, attrs }) {
+    let shouldReshow = false;
     const show = ref(false);
     const root = ref<HTMLElement>();
     const scrollParent = ref<Window | Element>();
@@ -116,6 +119,22 @@ export default defineComponent({
     useEventListener('scroll', throttle(scroll, 100), { target: scrollParent });
 
     onMounted(updateTarget);
+
+    onActivated(() => {
+      if (shouldReshow) {
+        show.value = true;
+        shouldReshow = false;
+      }
+    });
+
+    onDeactivated(() => {
+      // teleported back-top should be hide when deactivated
+      if (show.value && props.teleport) {
+        show.value = false;
+        shouldReshow = true;
+      }
+    });
+
     watch(() => props.target, updateTarget);
 
     return () => {