How we can validate the required fields? about pdftron-sign-app HOT 2 CLOSED

WebViewer(/* ... */).then(instance => {
  const { documentViewer, annotationManager, Annotations } = instance.Core;

  const checkIfAllRequiredFieldsAreFilled = (field) => {
    const { value, type, widgets } = field;
    if (type === 'Sig' && widgets[0].annot) {
      // Logic for when a required Signature field has not been filled goes here
    }
    if (
      field.flags.get(Annotations.WidgetFlags.REQUIRED)
      && (
        // For Textboxes, Comboboxes, Listboxes
        value === ''
        // For Checkboxes or Radiobuttons
        || value === 'Off'
      )
    ) {
      // Logic for when a required field has not been filled goes here
    }
    // Check children fields
    field.children.forEach(checkIfAllRequiredFieldsAreFilled);
  }

  documentViewer.addEventListener('annotationsLoaded', () => {
    // Please ensure the annotationsLoaded event has fired before invoking the
    // checkIfAllRequiredFieldsAreFilled method like below
    const fieldManager = annotationManager.getFieldManager();
    fieldManager.forEachField(checkIfAllRequiredFieldsAreFilled);
  });
});