You have to execute script and use js to do it now. However, it seems you have to set the value to a number, then use js to add to it. If you don't, the js call treats it as a character and instead of adding via math, it adds as a character.
Such as I want to start with zero 0, then add 1 to it. If treated as character, it ends up as "10", but if treated as math/integer, it ends up as "1". Then if I add another 1 to it, as char "110" as integer "2".
I do this all the time as I have a simple jsp that will allow me to fire custom sql's against a db, then it returns the raw data in a simple table format that I can verify the contents of each cell. There's a very long winded way that I use this data, which has been made much more complicated by the new json format used in the .side files... but I'll deal with that eventually.
Anyway, here's a small snippet, I'm storing the value into a variable called "rowNum":

I start by setting rowNum to a 1 on line 67. Then on row 69, I add 1 to it. Row 7 is using that variable to validate the contents in row 2 of an html table via xpath.
Then I add one again to increment it to verify contents of row 3 in the table. And so on.
Hope that helps.