excel javascript api protect worksheet

1Excel.run(function (context) {
2    var activeSheet = context.workbook.worksheets.getActiveWorksheet();
3    activeSheet.load("protection/protected");
4
5    return context.sync().then(function() {
6        if (!activeSheet.protection.protected) {
7            activeSheet.protection.protect();
8        }
9    })
10}).catch(errorHandlerFunction);
11