pavelpressf

const arr = [
  {
    "firstName": "maks",
    "lastName": "jer",
    "email": "joy@joy",
    "phoneNumber": "0999561146",
    "events": [
      {
        "title": "go",
        "description": "out",
        "startDate": "2011-09-02T21:00:00.000Z",
        "endDate": "2012-09-02T21:00:00.000Z"
      }
    ],
    "eventsCount": 1
  },
  {
    "firstName": "test",
    "lastName": "test",
    "email": "test@test",
    "phoneNumber": "09899898",
    "eventsCount": 2,
    "events": [
      {
        "title": "go",
        "description": "out",
        "startDate": "2022-03-09T00:00:00.000Z",
        "endDate": "2022-04-09T00:00:00.000Z",
      },
      {
        "title": "lodash",
        "description": "introducint",
        "startDate": "2003-08-11T21:00:00.000Z",
        "endDate": "2004-12-24T00:00:00.000Z"
      }
    ],
  }
];

arr.forEach((item) => {
  if (item.events) {
    item.events.sort((a, b) => {
      const dateA = new Date(a.startDate);
      const dateB = new Date(b.startDate);
      return dateA - dateB;
    });
  }
});