Convert a German Date to a date taht can be parsed in JS

Thank you very much @Nesa Nurani !

Eventually I want to extract just the year from of a date, so I can calculate the age of a building [year of the start-date (Beginn) - year of construction (Baujahr)] The Baujahr is delivered as a 4-digit number = the year, not as a date.

But I even have trouble to use your commands. When I tried your command in the console it seemingly did work fine:

I've changed the date and tried the same thing with variable, seems okay:

I've changed the date again and - but the console kept on working with the old date:

No matter what I tried, the date stuck to 10/12/2023 ...

I closed the form (and later the program too) and now the commands don't even recognize the date any more ...??

I was interrupted for a while and started all over again. Now without the Variable it worked fine, even with dates changed:

But trying to use the variable again -> undefined ... 

That's something that gives me a lot of trouble. It seems that Acrobat has some kind of cache that isn't handled properly ... the same form on the same computer with same datas sometimes works and sometimes fails, and no idea why. Okay the forms I'm working on are not in best shape, and I also have to admit, that I'm not an IT-expert, but I also work with SQL and SPL (a rather ancient derivative of C) and I always could rely, that same data, same script at least produces the same error ...