updated docs

Signed-off-by: Nwusongqing <wusongqing@huawei.com>

en/application-dev/reference/apis/js-apis-formextension.md

 # FormExtension
 
-> ![icon-note.gif](public_sys-resources/icon-note.gif) **Note:**
+> ![icon-note.gif](public_sys-resources/icon-note.gif) **NOTE**
 > The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.
 
 Provides **FormExtension** APIs.
@@ -42,6 +42,7 @@ Called to notify the widget provider that a **Form** instance (widget) has been
 - Example
 
   ```
+  export default class MyFormExtension extends FormExtension {
       onCreate(want) {
           console.log('FormExtension onCreate, want:' + want.abilityName);
           let dataObj1 = {
@@ -51,6 +52,7 @@ Called to notify the widget provider that a **Form** instance (widget) has been
           let obj1 = formBindingData.createFormBindingData(dataObj1);
           return obj1;
       }
+  }
   ```
 
 ## onCastToNormal
@@ -68,9 +70,11 @@ Called to notify the widget provider that a temporary widget has been converted
 - Example
 
   ```
+  export default class MyFormExtension extends FormExtension {
       onCastToNormal(formId) {
           console.log('FormExtension onCastToNormal, formId:' + formId);
       }
+  }
   ```
 
 ## onUpdate
@@ -88,6 +92,7 @@ Called to notify the widget provider that a widget has been updated. After obtai
 - Example
 
   ```
+  export default class MyFormExtension extends FormExtension {
       onUpdate(formId) {
           console.log('FormExtension onUpdate, formId:' + formId);
           let obj2 = formBindingData.createFormBindingData({temperature:"22c", time:"22:00"});
@@ -97,6 +102,7 @@ Called to notify the widget provider that a widget has been updated. After obtai
               }).catch((error) => {
               console.error('Operation updateForm failed. Cause: ' + error);});
       }
+  }
   ```
 
 ## onVisibilityChange
@@ -114,6 +120,7 @@ Called to notify the widget provider of the change of visibility.
 - Example
 
   ```
+  export default class MyFormExtension extends FormExtension {
       onVisibilityChange(newStatus) {
           console.log('FormExtension onVisibilityChange, newStatus:' + newStatus);
           let obj2 = formBindingData.createFormBindingData({temperature:"22c", time:"22:00"});
@@ -127,6 +134,7 @@ Called to notify the widget provider of the change of visibility.
                   console.error('Operation updateForm failed. Cause: ' + error);});
           }
       }
+  }
   ```
 
 ## onEvent
@@ -145,9 +153,11 @@ Called to instruct the widget provider to receive and process the widget event.
 - Example
 
   ```
+  export default class MyFormExtension extends FormExtension {
       onEvent(formId, message) {
           console.log('FormExtension onEvent, formId:' + formId + ", message:" + message);
       }
+  }
   ```
 
 ## onDestroy
@@ -165,7 +175,9 @@ Called to notify the widget provider that a **Form** instance (widget) has been
 - Example
 
   ```
+  export default class MyFormExtension extends FormExtension {
       onDestroy(formId) {
           console.log('FormExtension onDestroy, formId:' + formId);
       }
+  }
   ```