Improve isInstanceOf

src/dom_components/index.ts

@@ -522,7 +522,7 @@ export default class ComponentManager extends ItemManagerModule<DomComponentsCon
     const extendType = this.getType(extend!);
     const extendViewType = this.getType(extendView!);
     const typeToExtend = extendType ? extendType : compType ? compType : this.getType('default');
-    const modelToExt = typeToExtend.model;
+    const modelToExt = typeToExtend.model as typeof Component;
     const viewToExt = extendViewType ? extendViewType.view : typeToExtend.view;
 
     // Function for extending source object methods
@@ -543,12 +543,16 @@ export default class ComponentManager extends ItemManagerModule<DomComponentsCon
     if (typeof model === 'object') {
       const modelDefaults = { defaults: model.defaults };
       delete model.defaults;
+      const typeExtends = new Set(modelToExt.typeExtends);
+      typeExtends.add(modelToExt.getDefaults().type);
+
       methods.model = modelToExt.extend(
         {
           ...model,
           ...getExtendedObj(extendFn, model, modelToExt),
         },
         {
+          typeExtends,
           isComponent: compType && !extendType && !isComponent ? modelToExt.isComponent : isComponent || (() => 0),
         }
       );

src/dom_components/model/Component.ts

@@ -1771,7 +1771,10 @@ export default class Component extends StyleableModel<ComponentProperties> {
 
     if (!cmp) return false;
 
-    return this instanceof cmp;
+    // A tiny hack to make isInstanceOf work properly where there a multiple inheritance
+    const { typeExtends } = this.constructor as typeof Component;
+
+    return this instanceof cmp || typeExtends.has(type);
   }
 
   /**
@@ -1861,6 +1864,8 @@ export default class Component extends StyleableModel<ComponentProperties> {
     selector && selector.set({ name: id, label: id });
   }
 
+  static typeExtends = new Set<string>();
+
   static getDefaults() {
     return result(this.prototype, 'defaults');
   }