[improvement] optimize watch options (#4075)

src/mixins/popup/index.js

@@ -62,9 +62,7 @@ export const PopupMixin = {
       this.$emit(type);
     },
 
-    overlay() {
-      this.renderOverlay();
-    }
+    overlay: 'renderOverlay'
   },
 
   mounted() {

src/mixins/portal.ts

@@ -20,9 +20,7 @@ export function PortalMixin({ afterPortal }: PortalMixinOptions) {
     },
 
     watch: {
-      getContainer() {
-        this.portal();
-      }
+      getContainer: 'portal'
     },
 
     mounted() {