chore(ImagePreview): improve watcher

src/image-preview/ImagePreview.js

@@ -112,6 +112,8 @@ export default createComponent({
   },
 
   watch: {
+    startPosition: 'setActive',
+
     value(val) {
       if (val) {
         this.setActive(+this.startPosition);
@@ -126,10 +128,6 @@ export default createComponent({
       }
     },
 
-    startPosition(val) {
-      this.setActive(val);
-    },
-
     shouldRender: {
       handler(val) {
         if (val) {