Add layerCreated callback

Author: m-mohr

basemaps.config.js

@@ -7,6 +7,9 @@ const XYZ = 'XYZ';
 
 // All options (except for 'is') follow the OpenLayers options for the respective source class.
 // Projections (except for EPSG:3857 and EPSG:4326) must be listed in the `crs` array in the config.js.
+//
+// There's a layerCreated callback that can be used to modify the layer and source after it has been created:
+// async layerCreated(Layer layer, Source source) => Layer
 const BASEMAPS = {
   earth: [
     {

src/components/maps/MapMixin.js

@@ -140,11 +140,16 @@ export default {
             import(`ol/source/${options.is}.js`),
             import(`ol/layer/${layerClassName}.js`)
           ]);
-          return new layerCls({
-            source: new sourceCls(options),
+          const source = new sourceCls(options);
+          const layer = new layerCls({
+            source,
             title: options.title,
             base: true
           });
+          if (options.layerCreated) {
+            return await options.layerCreated(layer, source);
+          }
+          return layer;
         } catch (error) {
           console.error(`Failed to load basemap source for ${options.is}`, error);
           return null;