sources and layers.

src/ol/source/Image.js

@@ -38,6 +38,10 @@ export const ImageSourceEventType = {
   IMAGELOADERROR: 'imageloaderror',
 };
 
+/**
+ * @typedef {'imageloadend'|'imageloaderror'|'imageloadstart'} ImageSourceEventTypes
+ */
+
 /**
  * @classdesc
  * Events emitted by {@link module:ol/source/Image~ImageSource} instances are instances of this
@@ -89,6 +93,13 @@ class ImageSource extends Source {
       state: options.state,
     });
 
+    /***
+     * @type {import("../Observable").OnSignature<import("../Observable").EventTypes, import("../events/Event.js").default> &
+     *   import("../Observable").OnSignature<import("../ObjectEventType").Types, import("../Object").ObjectEvent> &
+     *   import("../Observable").OnSignature<ImageSourceEventTypes, ImageSourceEvent>}
+     */
+    this.on;
+
     /**
      * @private
      * @type {Array<number>}