Dropdown attribute with default value in WPBakery Visual Composer

vc-dropdown-item.php

<?php
/**
 * Visual Composer DropDown Item Example in Right Way
 * Dropdown attribute with default value in WPBakery Visual Composer
 * 
 * @package VC_Dropdown
 * @author Mahfuz <asrmahfuz8@gmail.com>
 */
vc_map(array(
      "name"        => __( "VC Dropdown", 'textdomain' ),
      "description" => __( "VC Dropdown items example in right way!!!", 'textdomain' ),
      "base"        => 'base_name',
      "controls"    => "full",
      "category"    => __( 'category_name', 'textdomain' ),
      "params"      => array(
          array(
              'type'          => 'dropdown',
              'heading'       => __( 'Dropdown Items', 'textdomain' ),
              'value'         => array(
                __( 'Item One', 'textdomain' )    => '1',
                __( 'Item Two', 'textdomain' )    => '2',
                __( 'Item Three', 'textdomain' )  => '3',
                __( 'Item Four', 'textdomain' )   => '4'
              ),
              'description'   => __( 'Upload member photo.', 'textdomain' ),
              'param_name'    => 'dropdown_items'
          )
      )
  )
);

It's a few years ago I wrote that bit of code.. but at time of writing it worked. Here you can read a tutorial about that topic with several comments of other people the code worked for as well:

https://urosevic.net/wordpress/tips/dropdown-defaults-visual-composer/

If I remember right that parameter was not documented years ago either but implemented nevertheless.