wp_ajax_closed_postboxes() WordPress Function

function wp_ajax_closed_postboxes() {
	check_ajax_referer( 'closedpostboxes', 'closedpostboxesnonce' );
	$closed = isset( $_POST['closed'] ) ? explode( ',', $_POST['closed'] ) : array();
	$closed = array_filter( $closed );

	$hidden = isset( $_POST['hidden'] ) ? explode( ',', $_POST['hidden'] ) : array();
	$hidden = array_filter( $hidden );

	$page = isset( $_POST['page'] ) ? $_POST['page'] : '';

	if ( sanitize_key( $page ) != $page ) {
		wp_die( 0 );
	}

	$user = wp_get_current_user();
	if ( ! $user ) {
		wp_die( -1 );
	}

	if ( is_array( $closed ) ) {
		update_user_meta( $user->ID, "closedpostboxes_$page", $closed );
	}

	if ( is_array( $hidden ) ) {
		// Postboxes that are always shown.
		$hidden = array_diff( $hidden, array( 'submitdiv', 'linksubmitdiv', 'manage-menu', 'create-menu' ) );
		update_user_meta( $user->ID, "metaboxhidden_$page", $hidden );
	}

	wp_die( 1 );
}