import { createStyleFunctionFromUrl, setMapProjection } from 'ol-esri-style';

// create a new vector layer
const vector = new VectorLayer({
  ...
});

// This is need for labeling features. Visible resolutions for the labels are calculated using map projection units.
setMapProjection(map.getView().getProjection());

// set layer style
createStyleFunctionFromUrl('arcgis_server_layer_url').then(styleFunction => {
  vector.setStyle(styleFunction);
});