test

console.time()
var users = {
  'userId1': {
    '01-02-2020': true,
    '02-02-2020': true
  },
  'userId2': {
    '02-02-2020': true
  },
  'userId3': {
    '03-02-2020': true
  },
  'userId4': {
    '04-02-2020': true
  }
};

var indexes = [...new Array(10).keys()]

var dates = indexes.map(i => moment().subtract(i, 'day').format('DD-MM-YYYY'));

var str = ''

Object.keys(users).map(id => {
  var user = users[id];
  var userDates = Object.keys(user);
  str += `${userDates}|`;
})

var result = dates.reduce((updates, date) => {
  updates[date] = str.split(date).length - 1;
  return updates;
}, Object.create(null))

console.timeEnd()
console.log(result, 'result')