How to find the code of the function that, when the page is loaded, processes the input data on the site?

Question

JavaScript

I'm trying to open Yandex maps. I see that there is an input encoded, it seems to be base64, however the standard base64 decoder from python3 stumbles over something.
How to find the code that processes the data?
I use FIREFOX
See here: https://old.maps.yandex.ru/?text=%D0%B0%D1%83%D0%B...
PS: Since among the answers I found a solution, a more general solution to the original question That original question has been rewritten to mark that decision as a decision.

Answer 1

Most likely the data is stored on the page in
Data loading goes in this method

onDataLoad: function(n, o) {
  n || (n = decodeURI(e.util.base64.from(t("#vpage")[0].text))),
  this.setPage(t.parseJSON(n), o)
},

If you take the decoding function directly from the site and play around with jsfiddle, then we will find your Audi-A3 Club service
Link to jsfiddle