Plot a featureCollection as a choropleth in Google Earth Engine (GEE)

choropleth.js

// bottom-left, top-right
var aoi = ee.Geometry.Rectangle(43.1, 13, 47, 30);

var ecoregions = ee.FeatureCollection('RESOLVE/ECOREGIONS/2017')
  .filterBounds(aoi);

var ecoregions_img = ecoregions
  .filter(ee.Filter.notNull(['SHAPE_AREA']))
  .reduceToImage({
    properties: ['SHAPE_AREA'],
    reducer: ee.Reducer.first()
});

var area_values = ecoregions
  .filter(ee.Filter.greaterThan("SHAPE_AREA", 0))
  .aggregate_array("SHAPE_AREA");
print(area_values) // 0 - 72


Map.centerObject(ecoregions, 4)
Map.addLayer(ecoregions_img, {
  min: 0,
  max: 73,
  palette: ['FCFDBF', 'FDAE78', 'EE605E', 'B63679', '711F81', '2C105C']
});
Map.addLayer({eeObject: ecoregions.draw({color: 'black', strokeWidth: 1}), visParams: {}, opacity: 0.3});