group dates by week javascript

You can use moment().week() to get the week number of the year and then group by it, here is a working example, I used array.reduce to create a new object of dates grouped by the week number:

const dates = [
  "1396-10-11 09:07:21",
  "1396-10-10 10:03:51",
  "1396-10-07 02:07:02",
  "1396-11-27 08:02:45",
  "1396-11-19 01:02:32",
  "1396-12-01 22:13:21",
  "1396-02-12 09:07:21",
  "1396-05-18 04:02:29",
  "1396-05-21 14:01:42",
  "1396-07-11 01:16:29"
];

const groups = dates.reduce((acc, date) => {

  // create a composed key: 'year-week' 
  const yearWeek = `${moment(date).year()}-${moment(date).week()}`;
  
  // add this key as a property to the result object
  if (!acc[yearWeek]) {
    acc[yearWeek] = [];
  }
  
  // push the current date that belongs to the year-week calculated befor
  acc[yearWeek].push(date);

  return acc;

}, {});

console.log(groups);

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.20.1/moment.min.js"></script>

Another simple way of achieving the same with Lodash would be as follows:

const groupBy = require('lodash/groupBy');
const moment = require('moment');
const data = [
   "1396-10-11 09:07:21",
   "1396-10-10 10:03:51",
   "1396-10-07 02:07:02",
   "1396-11-27 08:02:45",
   "1396-11-19 01:02:32",
   "1396-12-01 22:13:21",
   "1396-02-12 09:07:21",
   "1396-05-18 04:02:29",
   "1396-05-21 14:01:42",
   "1396-07-11 01:16:29"
];

groupBy(data, (dt) => moment(dt).week());

Result is as follows:

{ 
  '7': [ '1396-02-12 09:07:21' ],
  '21': [ '1396-05-18 04:02:29', '1396-05-21 14:01:42' ],
  '29': [ '1396-07-11 01:16:29' ],
  '41': [ '1396-10-07 02:07:02' ],
  '42': [ '1396-10-11 09:07:21', '1396-10-10 10:03:51' ],
  '47': [ '1396-11-19 01:02:32' ],
  '49': [ '1396-11-27 08:02:45', '1396-12-01 22:13:21' ] 
}