I have implemented the answer of Noel Gorelick to the question: Earth Engine get dates from imageCollection It is the following code:

var dates = s1_collection_f
    .map(function(image) {
      return ee.Feature(null, {'date': image.date().format('YYYY-MM-dd')})

It successfully returned a list of dates in the format 'YYYY-MM-dd', but I cannot read that list. I need to get every single date to be joined in the layers names. It seems to be weird, but I can't loop through the elements of the list. I have tried the following:

  1. The console returns for each element of the list:

    for (var index in dates) { print(dates[index]); }

  2. Nothing is returned:

    for (var i=0; i< dates.length(); i++) { print(dates[i]); }

How can I loop through the list and get each date?

  • 1
    The use of for-loops is discouraged in Earth Engine. You should use map method with dates list instead.
    – xunilk
    Jul 19, 2022 at 14:42

1 Answer 1


Following code is an example for joining layers names to every single date, in an arbitrarily selected ('COPERNICUS/S1_GRD') Image Collection, by using map instead a for loop.

var pt = ee.Geometry.Point(-104.18, 40.47); 

//Load S1 ImageCollection and filter by Location and Date
var s1_collection = ee.ImageCollection('COPERNICUS/S1_GRD')
  .filterDate('2017-01-01', '2018-01-01')

var s1_collection_lst = s1_collection.toList(s1_collection.size());

var names = s1_collection_lst.map(function (img)  {
  return ee.Image(img).id().slice(0, 17);


var dates = s1_collection.aggregate_array("system:time_start");

dates = dates.map(function (ele) {
  return ee.Date(ele).format().slice(0,10);

var paired = names.zip(dates);

var join_name_date = paired.map(function (ele) {
  return ee.String(ee.List(ele).get(0)).cat(ee.List(ele).get(1));


Script can be ran in following link.

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