How to extract year only from email date - date

Question

I'm reading an entire Gmail emails (inbox/sent/trash...), and try to create folders in google drive according to dates.
So folders should be categorized like (...,2019,2020, 2021). Each folder contains all emails in this year in my Gmail.
I managed to create the folders, getting messages through using Threads, all these things works fine, but I couldn't extract the year of the message only.
As when I use Threads[0].getMessages()[0].getDate() what is returned is date and time of this message. which I can't extract the year only from it.
I tried to split the date, but this is not string.
I tried to make smth like Threads[0].getMessages()[0].getDate().getYear() it returned 120!!!
I tried to see if I can access it as an array, [index], it returned null
I tried to parse it to Date(), but I couldn't get use of it too.
Is there is anyway that allows me to extract only the year from this format.
This is part of the script where i'm trying to fetch the date I'm using.
function GetAttachmentsWithTime() {
var sheet = SpreadsheetApp.getActiveSpreadsheet();
sheet.setActiveSheet(sheet.getSheetByName('Sheet1'));
var start = 0;
var end = 10;
var filter = "has:attachment";
var threads = GmailApp.search(filter,start,end);
Logger.log(threads[0].getMessages()[0].getDate())
}

Answer 1

Are you using the V8 runtime?
If so, see this migration guide. It says:
In the V8 runtime, Date.prototype.getYear() returns the year minus
1900 instead as required by ECMAScript standards.
So emails from the year 2020 would return 120 (i.e. 2020 - 1900 = 120).
To fix this, use .getFullYear():
When migrating your script to V8, always use
Date.prototype.getFullYear(), which returns a four-digit year
regardless of the date.