Get the same day of the week in a previous year

same_day_previous_year.js

// get same day of the week in the last x years ago for specific date.
// Default is 1 year ago, and default date is today, takes account of leap year
function getPreviousYearSameDay(dateToStart = false, years = 1) {
    const date = dateToStart ? new Date(dateToStart) : new Date();
    const lastYear = new Date(date.getFullYear() - years, date.getMonth(), date.getDate());
    const dayDiff = date.getDay() - lastYear.getDay();
    return new Date(lastYear.setDate(date.getDate() + dayDiff));
}

console.log(getPreviousYearSameDay('2024-10-10', 1).toISOString()); // 2023-10-11T23:00:00.000Z