identifier not found 'SizeOf'

WEB TMS WEB Core
1

I wanted to use SizeOf but I am getting a compilation error:


[Error] Unit1.pas (28, 7): identifier not found "SizeOf"

This comes from an empty TMS Web Application with the following FormCreate method:

procedure TForm2.WebFormCreate(Sender: TObject);
var x : integer;
begin
  x := sizeof (x);
end;

I noticed sizeof is used in some other TMS source files so I assumed I could used it. Using the latest stable release of TMS on Delphi 10.3 Up2. 
2

SizeOf() doesn't exist in pas2js compiler and it also doesn't make sense in JavaScript as it has no fixed size data types.