wp_ajax_add_link_category( string $action )

function wp_ajax_add_link_category( $action ) {
	if ( empty( $action ) )
		$action = 'add-link-category';
	check_ajax_referer( $action );
	$tax = get_taxonomy( 'link_category' );
	if ( ! current_user_can( $tax->cap->manage_terms ) ) {
		wp_die( -1 );
	}
	$names = explode(',', wp_unslash( $_POST['newcat'] ) );
	$x = new WP_Ajax_Response();
	foreach ( $names as $cat_name ) {
		$cat_name = trim($cat_name);
		$slug = sanitize_title($cat_name);
		if ( '' === $slug )
			continue;

		$cat_id = wp_insert_term( $cat_name, 'link_category' );
		if ( ! $cat_id || is_wp_error( $cat_id ) ) {
			continue;
		} else {
			$cat_id = $cat_id['term_id'];
		}
		$cat_name = esc_html( $cat_name );
		$x->add( array(
			'what' => 'link-category',
			'id' => $cat_id,
			'data' => "<li id='link-category-$cat_id'><label for='in-link-category-$cat_id' class='selectit'><input value='" . esc_attr($cat_id) . "' type='checkbox' checked='checked' name='link_category[]' id='in-link-category-$cat_id'/> $cat_name</label></li>",
			'position' => -1
		) );
	}
	$x->send();
}