chore: add getZIndexStyle util (#8254)

src/index-bar/index.tsx

@@ -85,19 +85,19 @@ export default createComponent({
 
     linkChildren({ props });
 
-    const sidebarStyle = computed(() => {
+    const sidebarStyle = computed<CSSProperties | undefined>(() => {
       if (isDef(props.zIndex)) {
         return {
           zIndex: +props.zIndex + 1,
-        } as CSSProperties;
+        };
       }
     });
 
-    const highlightStyle = computed(() => {
+    const highlightStyle = computed<CSSProperties | undefined>(() => {
       if (props.highlightColor) {
         return {
           color: props.highlightColor,
-        } as CSSProperties;
+        };
       }
     });
 

src/index-bar/test/__snapshots__/demo.spec.ts.snap

@@ -870,9 +870,7 @@ exports[`should render demo and match snapshot 1`] = `
         </div>
         <div>
           <div style="height: 0px;">
-            <div class="van-index-anchor van-index-anchor--sticky van-hairline--bottom"
-                 style="z-index: undefined;"
-            >
+            <div class="van-index-anchor van-index-anchor--sticky van-hairline--bottom">
               Z
             </div>
           </div>

src/index-bar/test/__snapshots__/index.spec.js.snap

@@ -300,9 +300,7 @@ exports[`should update active anchor after page scroll 2`] = `
   <div data-index="0"
        style="height: 10px;"
   >
-    <div class="van-index-anchor van-index-anchor--sticky van-hairline--bottom"
-         style="z-index: undefined;"
-    >
+    <div class="van-index-anchor van-index-anchor--sticky van-hairline--bottom">
       1
     </div>
   </div>
@@ -310,7 +308,7 @@ exports[`should update active anchor after page scroll 2`] = `
        style="height: 10px;"
   >
     <div class="van-index-anchor van-index-anchor--sticky van-hairline--bottom"
-         style="z-index: undefined; transform: translate3d(0, 10px, 0);"
+         style="transform: translate3d(0, 10px, 0);"
     >
       2
     </div>