google earth engine - 10 days composite from Sentinel 2 Images Collection

A monthly composite can be made using the following code, I take example from Sentinel 2 L1C:

var geometry = ee.Geometry.Point([109.061, 11.78]); 
var col = ee.ImageCollection('COPERNICUS/S2')
          .filterBounds(geometry).filterDate('2018-01-01','2019-01-01');
//Monthly Images
var months = ee.List.sequence(1,12);
var years = ee.List.sequence(2018,2018); 

// monthly composite
var monthlyImages =  ee.ImageCollection.fromImages(
  years.map(function (y) {
  return months.map(function(m){
  var w = col.select('B1').filter(ee.Filter.calendarRange(y, y, 'year'))
           .filter(ee.Filter.calendarRange(m, m, 'month'))
           .mean()
           //.median()
           //.min()
           .set('system:time_start',ee.Date.fromYMD(y,m,1));

  return w.set('year', y)
           .set('month', m)
           .set('date', ee.Date.fromYMD(y,m,1))
           .set('system:time_start',ee.Date.fromYMD(y,m,1)) 

});
}).flatten());

print(monthlyImages)

How do I do a decadal composite (every 10 days)?