Incorrect calculation date

[Václav Petrák]

Hello,
I need to calculate the date by subtracting one day from the date I know. It only works well if it is not the first day of the year.

var timeZone = Session.getScriptTimeZone();
var MILLIS_PER_DAY = 1000 * 60 * 60 * 24;
var day= new Date(2021, 0, 1);var yesterday = new Date(day.getTime() - MILLIS_PER_DAY);

Logger.log(Utilities.formatDate(day, timeZone, "dd.MM.YYYY"));//return 01.01.2021

Logger.log(Utilities.formatDate(yesterday, timeZone, "dd.MM.YYYY"));//return 31.12.2021

The script then sets the last day of the year, but the year is incorrect!
Please, how can I solve this?
Thank you sorry for by bad English

[Andrew Roberts]

Weird! I can only guess you've found a bug in formatDate. I tried logging the values for different years and timezones and the yesterday date object is OK, it's just not formatting OK.

[dimud...@gmail.com]

NEVER use the upper-case "YYYY" formatter. ALWAYS use the lower-case "yyyy" formatter.

The following script will work as expected.

function testFormatDate() {

    var timeZone = Session.getScriptTimeZone();
    var MILLIS_PER_DAY = 1000 * 60 * 60 * 24;
    var day= new Date(2021, 0, 1);

    var yesterday = new Date(day.getTime() - MILLIS_PER_DAY);

    Logger.log(Utilities.formatDate(day, timeZone, "dd.MM.yyyy"));

    Logger.log(Utilities.formatDate(yesterday, timeZone, "dd.MM.yyyy"));