(ArcGIS API for JavaScript) Sample of simplifying polygons using 4.x

Sample.js

require([
    "esri/Map",
    "esri/views/MapView",
    "esri/layers/FeatureLayer",
    "esri/tasks/support/Query",
    "esri/tasks/QueryTask",
    "esri/geometry/geometryEngineAsync",
    "dojo/domReady!"
  ],
  function (Map, MapView, FeatureLayer, Query, QueryTask, geometryEngineAsync) {

    let verticesLayer = new FeatureLayer({
      url: "url to feature layer"
    });

    //Create a new map and set the basemap to Dark gray
    var map = new Map({
      basemap: "dark-gray",
    });

    //set a new view and set the properties of the view
    var view = new MapView({
      container: "viewDiv",
      map: map,
      center: [-86.049, 38.485],
      zoom: 3
    });

    //Setting up the renderer
    var citiesRenderer = {
      type: "simple",
      symbol: {
        type: "simple-fill",
        size: 6,
        color: "black",
        outline: {
          width: 0.5,
          color: "white"
        }
      }
    };

    //Setting up the query 
    var query = new Query();
    query.where = "1=1";
    query.outFields = ["*"];
    query.maxAllowableOffset = 10;
    query.returnGeometry = true;


    //After the layer loads, run a query on the layer, then loop through each layer and simplify each geometry. Then replace each geometry with the query results.
    verticesLayer.load().then(() => {
      verticesLayer.queryFeatures(query).then((results) => {
        results.features.forEach((element) => {
          //geometryEngineAsync.generalize(element.geometry, 7, true) - for a more defined method
          geometryEngineAsync.simplify(element.geometry).then((genResults) => {
            results.features.geometry = genResults;
          });
        }, this);

        //Create a new feature layer with the simplified geometries
        let myfeaturelayer = new FeatureLayer({
          source: results.features,
          fields: results.fields,
          objectIdField: "ObjectID",
          geometryType: results.geometryType,
          spatialReference: results.spatialReference,
          renderer: citiesRenderer
        });
        map.add(myfeaturelayer);
      });
    });



  });