I was looking for a method to filter the Identify results and after digging into the obfuscated code of the API I found out that there are some properties in the IdentifyParameters which are not documented. One of them is the property "layerDefinitions" and that was exactly what I was looking for!
Unfortunately the Typescript definitions do not expose these properties and also the documentation do not mention them. I was wondering why these properties are not documented and in the definition file.
My workaround for now is:
const params = new IdentifyParameters();
params.width = this.view.width;
params.height = this.view.height;
params.mapExtent = this.view.extent;
params.layerOption = 'visible';
params.geometry = geometry;
params.tolerance = 3;
params.returnGeometry = true;
params.returnFieldName = true;
// Undocumented property...
(params as any).layerDefinitions = myLayerDefinitions // format: {layerId1: whereClause1, layerId2: whereClause2}
Hopefully the properties will soon be added to the definitions file and documentation.