Add data attribute with variable term_id to wp_list_categories

functions.php

<?php 

/*========================================================================
Filter wp_list_categories to add new attribute
========================================================================*/
add_filter('wp_list_categories','moons_ajax_onclick');
function moons_ajax_onclick($output){
  //if (is_post_type_archive('crew')) { // localize this filter if needed 
  
  //if not using a CPT then change get_terms to get_categories	
  $terms = get_terms( array(
  	    'taxonomy' => 'crew_category',
  	));
    // cycle through the terms
  	foreach($terms as $term) {
  		$term_id = $term->term_id;
  
  		$pattern = '/' . $term_id . '"><a/';		
      // onclick is the new attribute, use or change as needed
  		$replacement = $term_id . '"><a class="' . $term_id . '" onclick="term_ajax_get(\'' . $term->term_id . '\')" ';
  		$output = preg_replace( $pattern, $replacement, $output );
  	}
  	return $output;
  /*} else {
    return $output; //output for everything else
  }*/
}