A rookie here.
Messing with my google scripts projects I have found a strange thing, a method that I was using was strike-through in the editor and it looked like this --> substr
At first, I had no problem with this, but, if it was not there before, and it is now, that means that the version of javascript that my project is using is changing and I do not want that. And there is my question
Is there a way to make the version of V8 JavaScript that my google script uses constant?
Looking in to the app-scripts documentation I have found that it uses V8 and that it is defined in the manifest but the way of freezing to a certain version is nowhere to be found. Maybe there is an easy answer, but I have no clue where else to look. Any help will be welcomed.
No, there is no way to select a particular V8 version for your GAS.
That said, JavaScript engines are generally very conscious of backwards compatibility. It is extremely rare that features are removed -- there are a good number of "legacy"/"deprecated" things in JS that won't be removed for the foreseeable future, because there's too much old and unmaintained (but still used) code out there that depends on them, and browser makers don't want to break that code.
Regarding the specific case at hand, I personally would be quite surprised if String.prototype.substr ever got removed. I see its deprecation as more of a "pro tip: how not to confuse substr and substring: only ever use one of them".
FWIW, V8 itself has no notion of deprecated JavaScript features. The strike-through you see is just an editor feature. Updating or not updating the V8 version underneath wouldn't affect it.
Taking a step back: writing software once and then expecting it to work without maintenance or monitoring for decades is, unfortunately, generally not a thing. For instance, if you developed a game for Windows 95, you'd have to expect that it won't run well (or not at all) on modern Windows versions. There are countless more examples of operating systems, SDKs/toolkits, compilers/engines, and programming languages themselves evolving over time in ways that guarantee backwards-compatibility for a couple of years but not forever. This is the flip side of technological progress. Pinning yourself to certain outdated versions is generally not a viable solution, for a variety of reasons.
So actually, in comparison, when you write an app or script in JavaScript, you have a very high chance of it still working fine 20 years later. So I wouldn't worry about it too much.