如何从数组中获取唯一的年份？

function getUniqueYearsFromArray(arr) {
  var uniqueYears = [];
  
  for (var i = 0; i < arr.length; i++) {
    var year = arr[i].getFullYear();
    
    if (uniqueYears.indexOf(year) === -1) {
      uniqueYears.push(year);
    }
  }
  
  return uniqueYears;
}

var dates = [
  new Date('2022-01-01'),
  new Date('2022-02-01'),
  new Date('2022-03-01'),
  new Date('2021-01-01'),
  new Date('2021-02-01')
];

var uniqueYears = getUniqueYearsFromArray(dates);
console.log(uniqueYears); // [2022, 2021]