diff --git a/src/composition/use-visibility-change.ts b/src/composition/use-visibility-change.ts
index 2de6d4430..f7bec82fc 100644
--- a/src/composition/use-visibility-change.ts
+++ b/src/composition/use-visibility-change.ts
@@ -9,7 +9,7 @@ import {
 
 // @Experimental
 export function useVisibilityChange(
-  target: Ref<Element>,
+  target: Ref<Element | undefined>,
   onChange: (visible: boolean) => void
 ) {
   // compatibility: https://caniuse.com/#feat=intersectionobserver
@@ -26,11 +26,15 @@ export function useVisibilityChange(
   );
 
   const observe = () => {
-    observer.observe(target.value);
+    if (target.value) {
+      observer.observe(target.value);
+    }
   };
 
   const unobserve = () => {
-    observer.unobserve(target.value);
+    if (target.value) {
+      observer.unobserve(target.value);
+    }
   };
 
   onMounted(observe);
diff --git a/src/sticky/index.js b/src/sticky/index.tsx
similarity index 83%
rename from src/sticky/index.js
rename to src/sticky/index.tsx
index d1943290d..572e42e49 100644
--- a/src/sticky/index.js
+++ b/src/sticky/index.tsx
@@ -1,4 +1,4 @@
-import { ref, reactive, computed } from 'vue';
+import { ref, reactive, computed, CSSProperties } from 'vue';
 
 // Utils
 import {
@@ -28,7 +28,7 @@ export default createComponent({
   emits: ['scroll'],
 
   setup(props, { emit, slots }) {
-    const root = ref();
+    const root = ref<HTMLElement>();
     const scrollParent = useScrollParent(root);
 
     const state = reactive({
@@ -39,24 +39,24 @@ export default createComponent({
 
     const offsetTop = computed(() => unitToPx(props.offsetTop));
 
-    const style = computed(() => {
+    const style = computed<CSSProperties | undefined>(() => {
       if (!state.fixed) {
         return;
       }
 
-      const top = offsetTop.value ? `${offsetTop.value}px` : null;
+      const top = offsetTop.value ? `${offsetTop.value}px` : undefined;
       const transform = state.transform
         ? `translate3d(0, ${state.transform}px, 0)`
-        : null;
+        : undefined;
 
       return {
         top,
-        zIndex: props.zIndex,
+        zIndex: props.zIndex !== undefined ? +props.zIndex : undefined,
         transform,
       };
     });
 
-    const emitScrollEvent = (scrollTop) => {
+    const emitScrollEvent = (scrollTop: number) => {
       emit('scroll', {
         scrollTop,
         isFixed: state.fixed,
@@ -64,7 +64,7 @@ export default createComponent({
     };
 
     const onScroll = () => {
-      if (isHidden(root)) {
+      if (!root.value || isHidden(root)) {
         return;
       }
 
@@ -104,13 +104,12 @@ export default createComponent({
     };
 
     useEventListener('scroll', onScroll, { target: scrollParent });
-
     useVisibilityChange(root, onScroll);
 
     return () => {
       const { fixed, height } = state;
-      const rootStyle = {
-        height: fixed ? `${height}px` : null,
+      const rootStyle: CSSProperties = {
+        height: fixed ? `${height}px` : undefined,
       };
 
       return (