function assets() {
  // enqueue your script
  wp_enqueue_script('handle', get_template_directory_uri() . '/path/to/main.js', ['jquery'], '$ver', true);
  // localize script
  wp_localize_script('handle', 'custom_ajaxify', array( 'ajaxurl' => admin_url( 'admin-ajax.php' ) ) );
}
add_action('wp_enqueue_scripts', 'assets', 100);

/**
 * AJAX load template part
 */
function ajax_load_posts() {
    global $post;
    
    // Get the queryVars sent over from the AJAX request
    $query_vars = $_POST['queryVars'];
    
    $args = array(
        'post_type'      => $query_vars['post_type'],
        'posts_per_page' => $query_vars['posts_per_page'],
        'offset'         => $query_vars['offset'],
        'update_post_term_cache' => false, // Improves Query performance
        'update_post_meta_cache' => false, // Improves Query performance
    );
    $posts = get_posts($args);

    // The array of data we will return to the AJAX call
    $payload = array(
        'posts' => array(),
        'query_vars' => $query_vars // Here for debugging purposes so we can console.log later
    );

    if ( $posts ) :
        foreach ( $posts as $post ) : setup_postdata( $post );
            // Use object buffering to send each post as a separate string instead of all at once.
            ob_start();
            get_template_part('templates/list-item', get_post_type());
            array_push($payload['posts'], ob_get_clean() );
        endforeach;
        wp_reset_postdata();    
    endif;

    // We always send some data, even if there are no posts.
    echo json_encode($payload);
    die();
}
add_action('wp_ajax_nopriv_ajax_load_posts', 'ajax_load_posts');
add_action('wp_ajax_ajax_load_posts', 'ajax_load_posts');