Call function from dialog file

I write a plugin for replacing forms select with a fakeelement, because select is not editable. Now I have to set the values for dialog. This is what I have:

if ( dialogName == 'select' )
{
    dialogDefinition.onShow = function()
   {
      var selection = editor.getSelection(),
         element = selection.getSelectedElement();
      
      if ( element && element.data( 'cke-real-element-type' ) && element.data( 'cke-real-element-type' ) == 'selectfield' )
      {
         this.selectBox = element;
         element = editor.restoreRealElement( this.selectBox );
         this.setupContent( 'select', element );
         
         var objOptions = getOptions( element );
         for ( var i = 0 ; i < objOptions.count() ; i++ )
            this.setupContent( 'option', objOptions.getItem( i ) );
         
         selection.selectElement( this.selectBox );
      }
   };
}

I get the error getOptions is not defined
getOptions is a function in the original dialog file. How can I use this function in my plugin? I could copy all functions I need, but I think that makes no sense.