add a more extended emits definition

vue-cli-01-a-new-vue-project/src/components/FriendContact.vue

@@ -36,7 +36,16 @@ export default {
             default: false,
         },
     },
-    emits: ["toggle-favorite"],
+    emits: {
+        "toggle-favorite": function(id) {
+            if (id) {
+                return true;
+            } else {
+                console.warn("ID is missing!");
+                return false;
+            }
+        },
+    },
     data() {
         return {
             detailsAreVisible: false,