Javascript – In Apps Script, why does 1/1/2023 gets reset as 12/31/2022 whenever I try to do math using Date()?

• Background:
  I am pretty new to apps script, i have some beginner knowledge in other languages. I am trying to do some dates math, this happens in a loop when a user enters two dates (from and to) in cells. I am trying to iterate each date and enter some values in some cells.

• Issue:
  The user enters the value as "MM/DD/YYYY". However, when using 1/1/2023, this becomes as "Sat Dec 31 16:00:00 GMT-05:00 2022". Also, subtraction works fine (by the number of milli seconds in a day multiplied by the number of days to be subtracted), but the addition operation fails and returns the same value, which is "Sat Dec 31 16:00:00 GMT-05:00 2022".

• Other StackOverflow topics:
  I checked similar topics, but they had which got me to add trial 2 and 3, but my problem is specific to the 1/1/yyyy becoming 12/31/yyyy-1.

• The code:

function PlayGround() {  
    // setting variables
    var spreadsheet = SpreadsheetApp.getActive();
    const MILLIS_PER_DAY = 1000 * 60 * 60 * 24 * 5; // multiplied by 5 (5 days)
    const now = new Date();

    // trial 1
    const aDate = spreadsheet.getRange('J4').getValue()
    // J4 data type is set to date from the interface, and its value is equal to "1/1/2023"
    Logger.log(new Date(aDate));
    Logger.log(new Date(aDate - MILLIS_PER_DAY));
    Logger.log(new Date(aDate + MILLIS_PER_DAY));
    // function returns
    // 2:56:12 PM   Info    Sat Dec 31 16:00:00 GMT-05:00 2022
    // 2:56:12 PM   Info    Mon Dec 26 16:00:00 GMT-05:00 2022
    // 2:56:12 PM   Info    Sat Dec 31 16:00:00 GMT-05:00 2022

    // trial 2
    var new_d = Utilities.formatDate(new Date(aDate), "EET", "MM/dd/yyyy")
    Logger.log(new Date(new_d));
    Logger.log(new Date(new_d - MILLIS_PER_DAY));
    Logger.log(new Date(new_d + MILLIS_PER_DAY));
    // function returns
    // 3:14:35 PM   Info    Sat Dec 31 00:00:00 GMT-05:00 2022
    // 3:14:35 PM   Info    Wed Dec 31 19:00:00 GMT-05:00 1969
    // 3:14:35 PM   Info    Wed Dec 31 19:00:00 GMT-05:00 1969

    // trial 3
    const d = new Date(aDate);
    Logger.log(d);
    Logger.log(new Date(d.setDate(d.getDate() + 5)));
    Logger.log(new Date(d.setDate(d.getDate() - 5)));
    Logger.log(new Date(d.setDate(d.getDate() - 20)));
    // function returns
    // 3:14:35 PM   Info    Sat Dec 31 16:00:00 GMT-05:00 2022
    // 3:14:35 PM   Info    Thu Jan 05 16:00:00 GMT-05:00 2023
    // 3:14:35 PM   Info    Sat Dec 31 16:00:00 GMT-05:00 2022
    // 3:14:35 PM   Info    Sun Dec 11 16:00:00 GMT-05:00 2022
    // the -5 does not work, but - 20 works!!

    }