NetworkSystemLayers

require([
  "esri/WebMap",
  "esri/views/MapView",
  "esri/config"
], (WebMap, MapView, esriConfig) => {
  let utilityNetwork;

  // set the hostname to the portal instance
  esriConfig.portalUrl = "https://myHostName.domain.com/arcgis";

  const webMap = new WebMap({
    portalItem: {
      id: "webmapID"
    }
  });

  const mapView = new MapView({
    map: webMap
  });

  webMap.when(async () => {
    // check if webMap contains utility networks
    if (webMap.utilityNetworks.length > 0) {
      // assign the utility network at index 0
      utilityNetwork = webMap.utilityNetworks.at(0);

      // trigger the loading of the UtilityNetwork instance
      await utilityNetwork.load();

      // Print the subnetworks table service url and id
      console.log(`Dirty areas layer id: ${utilityNetwork.networkSystemLayers.subnetworksTableId}`);
      console.log(`Dirty areas layer url: ${utilityNetwork.networkSystemLayers.subnetworksTableUrl}`);
    }
  });
});