JS new Date() object is unexpectedly synchronised elsewhere

Question

I want to store two values in an object: today, todayInOneYear. I use a function to calculate the +1 year.

obj = {}
today = new Date();

obj = {
  today: today,
  oneYear: addOneYear(today)
}
console.log(obj)

function addOneYear(date) {
  date.setFullYear(date.getFullYear() + 1);
  return date;
}

Problem: Today and todayInOneYear are the same. But I expect two different dates. Once from now (today) and then once from a year from now. Do you know what I'm missing?

Answer 1

You'll need to clone the Date object:

obj = {}
today = new Date();

obj = {
  today: today,
  oneYear: addOneYear(today)
}
console.log(obj)

function addOneYear(date) {
  let clone = new Date(date);
  clone.setFullYear(clone.getFullYear() + 1);
  return clone;
}

Answer 2

You can try this code

obj = {}
today = new Date();

obj = {
  today: today,
  oneYear: addOneYear(today)
}
console.log(obj)
function addOneYear(date) {
  const aYearFromNow = new Date(date);
  aYearFromNow.setFullYear(aYearFromNow.getFullYear() + 1);
    console.log(aYearFromNow)
  return aYearFromNow;
}