Frontend AJAX Sub-Category Dropdown (Load sub-category dropdown based on parent category by ajax call)

sub_category_dropdown.php

<?php
/*
Plugin Name: Frontend AJAX Sub-Category Dropdown
Plugin URI: http://khaledsaikat.com
Description: Load sub-category dropdown based on parent category by ajax call
Version: 0.1
Author: Khaled Hossain
Author URI: http://khaledsaikat.com
*/


/**
 * Add shortcode [ajax-dropdown] to any post or page
 */

if ( ! class_exists( 'frontendAjaxDropdown' ) ):

    class frontendAjaxDropdown
    {
        /**
         * Loading WordPress hooks
         */
        function __construct()
        {
            /**
             * Add shortcode function
             */
            add_shortcode( 'ajax-dropdown', array($this, 'init_shortocde') );

            /**
             * Register ajax action
             */
            add_action( 'wp_ajax_get_subcat', array($this, 'getSubCat') );

            /**
             * Register ajax action for non loged in user
             */
            add_action('wp_ajax_nopriv_get_subcat', array($this, 'getSubCat') );
        }

        /**
         * Show parent dropdown for wordpress category and loaded necessarry javascripts
         */
        function init_shortocde()
        {
            wp_dropdown_categories(
                'name=main_cat&selected=-1&hierarchical=1&depth=1&hide_empty=0&show_option_none=All Categories'
            );

            ?>
            <script type="text/javascript">
                (function($){
                    $("#main_cat").change(function(){
                        $("#sub_cat").empty();
                    	$.ajax({
                    		type: "post",
                            url: "<?php echo admin_url( 'admin-ajax.php' ); ?>",
                            data: { action: 'get_subcat', cat_id: $("#main_cat option:selected").val() },
                    		beforeSend: function() {$("#loading").fadeIn('slow');},
                    		success: function(data) {
                                $("#loading").fadeOut('slow');
                                $("#sub_cat").append(data);
                    		}
                    	});
                    });
                })(jQuery);
            </script>

            <div id="loading" style="display: none;">Loading...</div>
            <div id="sub_cat"></div>
            <?php
        }

        /**
        * AJAX action: Shows dropdown for selected parent
        */
        function getSubCat()
        {
            wp_dropdown_categories(
                "name=sub_cat&selected=-1&hierarchical=1&depth=1&hide_empty=0&child_of={$_POST['cat_id']}"
            );

            die();
        }

    }

endif;

new frontendAjaxDropdown();

Khalid please help me
I am not able to use this plugin.
Can you please help me on teamviewer