added base element

app/elements/_base.ts

@@ -0,0 +1,18 @@
+export class BaseElement extends HTMLElement {
+    private _hasConnectedCallback: boolean = false;
+    connectedCallback() {
+
+        if (!this._hasConnectedCallback) {
+            this.onInit();
+        }
+        else {
+            this.onUpdate();
+        }
+
+        this._hasConnectedCallback = true;
+
+    }
+
+    onInit() { }
+    onUpdate() { }
+}