/*
Есть массив операций
Необходимо операции отсортировать по дате и сгруппировать их по году, а в качестве значений представить массивы с датами в формате MM-DD.
Пример результаты:
result = {
	"2017": [
		"07-31",
		"08-22"
		],
	"2018": [
		"01-01",
		"02-22"
	]
}
*/
 
const operations = [
  { date: "2017-07-31", amount: "5422" },
  { date: "2017-06-30", amount: "5220" },
  { date: "2017-05-31", amount: "5365" },
  { date: "2017-08-31", amount: "5451" },
  { date: "2017-09-30", amount: "5303" },
  { date: "2018-03-31", amount: "5654" },
  { date: "2017-10-31", amount: "5509" },
  { date: "2017-12-31", amount: "5567" },
  { date: "2018-01-31", amount: "5597" },
  { date: "2017-11-30", amount: "5359" },
  { date: "2018-02-28", amount: "5082" },
  { date: "2018-04-14", amount: "2567" },
];
 
function sortOperations(operations) {
  // Код функции здесь
}

function sortOperations(operations) {
  return operations.reduce((acc, el) => {
    const year = new Date(el.date).getFullYear();
    if (acc[year]) {
      acc[year].push(el.date.slice(5));
      acc[year].sort((a, b) => (a > b ? 1 : -1));
    } else {
      acc[year] = [el.date.slice(5)];
    }
    return acc;
  }, {});
}
 
console.log(sortOperations(operations));

function sortOperations(operations) {
  const operDate = {};
 
  for (let name of operations) {
    let date = new Date(name["date"]);
    let day = date.getDate();
    let month = date.getMonth() + 1;
    let year = date.getFullYear();
 
    if (month < 10) month = "0" + month;
    if (day < 10) day = "0" + day;
 
    if (operDate[year]) {
      operDate[year].push(`${month}-${day}`);
      operDate[year].sort((a, b) => (a > b ? 1 : -1));
    } else {
      operDate[year] = [`${month}-${day}`];
    }
  }
  return operDate;
}
 
console.log(sortOperations(operations));