make SimpleTile inherit from ViewModel

to use same update mechanism and have viewmodel infra available for tile

src/domain/ViewModel.js

@@ -70,6 +70,10 @@ export class ViewModel extends EventEmitter {
         return result;
     }
 
+    updateOptions(options) {
+        this._options = Object.assign(this._options, options);
+    }
+
     emitChange(changedProps) {
         if (this._options.emitChange) {
             this._options.emitChange(changedProps);

src/domain/session/room/timeline/tiles/GapTile.js

@@ -29,16 +29,16 @@ export class GapTile extends SimpleTile {
         // prevent doing this twice
         if (!this._loading) {
             this._loading = true;
-            this.emitUpdate("isLoading");
+            this.emitChange("isLoading");
             try {
                 await this._timeline.fillGap(this._entry, 10);
             } catch (err) {
                 console.error(`timeline.fillGap(): ${err.message}:\n${err.stack}`);
                 this._error = err;
-                this.emitUpdate("error");
+                this.emitChange("error");
             } finally {
                 this._loading = false;
-                this.emitUpdate("isLoading");
+                this.emitChange("isLoading");
             }
         }
     }

src/domain/session/room/timeline/tiles/MessageTile.js

@@ -62,7 +62,7 @@ export class MessageTile extends SimpleTile {
         const isContinuation = prev && prev instanceof MessageTile && prev.sender === this.sender;
         if (isContinuation !== this._isContinuation) {
             this._isContinuation = isContinuation;
-            this.emitUpdate("isContinuation");
+            this.emitChange("isContinuation");
         }
     }
 }

src/domain/session/room/timeline/tiles/SimpleTile.js

@@ -15,11 +15,12 @@ limitations under the License.
 */
 
 import {UpdateAction} from "../UpdateAction.js";
+import {ViewModel} from "../../../../ViewModel.js";
 
-export class SimpleTile {
+export class SimpleTile extends ViewModel {
     constructor({entry}) {
+        super();
         this._entry = entry;
-        this._emitUpdate = null;
     }
     // view model props for all subclasses
     // hmmm, could also do instanceof ... ?
@@ -38,12 +39,6 @@ export class SimpleTile {
         return false;
     }
 
-    emitUpdate(paramName) {
-        if (this._emitUpdate) {
-            this._emitUpdate(this, paramName);
-        }
-    }
-
     get internalId() {
         return this._entry.asEventKey().toString();
     }
@@ -53,7 +48,7 @@ export class SimpleTile {
     }
     // TilesCollection contract below
     setUpdateEmit(emitUpdate) {
-        this._emitUpdate = emitUpdate;
+        this.updateOptions({emitChange: paramName => emitUpdate(this, paramName)});
     }
 
     get upperEntry() {