How to convert lower case to upper case in Lumira designer .

I am using the below document with function UpperCase(String)

https://help.sap.com/viewer/Discovery_User_Guide/80e0391bec034350a5499cd3d8e02fab.html

I have one global variable

which store lumira user detail .

var user_id= Application.getinfo.user();

I want to conver user_id to upper case .

if I am using

var user_id1 =UpperCase(user_id);

its showing error .

error

Could not resolve reference to variable UpperCase();