How to get FeatureCollection column names

Question

I'm using a FeatureCollection and I would like to discover the column names as a ee.List. Looking at the documentation, I only find ways to reduce them but you need to know their names.

For example from:

var collection = ee.FeatureCollection([
  ee.Feature(ee.Geometry.Point(77.58, 13), {date:'2020-10-02', count:1, x:1}),
  ee.Feature(ee.Geometry.Point(77.58, 13), {date:'2020-10-04', count:1, x:1}),
  ee.Feature(ee.Geometry.Point(77.58, 13), {date:'2020-10-02', count:3, x:0}),
  ee.Feature(ee.Geometry.Point(77.58, 13), {date:'2020-10-01', count:2, x:0})
]);

I would like to extract

ee.List(["system:index", "date", "count", "x"])

Answer 1

If the collection is consistent (i.e. all features have the same properties) then you can do:

var columns = collection.first().propertyNames()

as shown in https://code.earthengine.google.com/a10ccab842d428904b1fe46f3aa71a17