[рони]

dc65k,

<pre>
  <script>
const arr = [
    { "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" }
];

 /* result = {
    "2017": [
      "07-31",
      "08-22"
    ],
    "2018": [
      "01-01"
      "02-22"
    ]
  } */
let result = arr.reduce((obj, {date}) => {
let [year, month, data] = date.split(/\-/);
data = `${[month, data].join('-')}`;
obj[year] ? obj[year].push(data) : (obj[year]=[data]);
obj[year].sort();
return obj
}, {})
document.write(JSON.stringify(result, "", 4))
  </script>
</pre>