annotations?

src/chess-circle.ts

@@ -0,0 +1,39 @@
+class ChessCircle extends HTMLElement {
+  connectedCallback() {
+    this._upgradeProperty("square");
+    this._upgradeProperty("color");
+  }
+
+  set square(square: string | null) {
+    if (square != null) {
+      this.setAttribute("square", square);
+    } else {
+      this.removeAttribute("square");
+    }
+  }
+  get square() {
+    return this.getAttribute("square");
+  }
+
+  set color(color: string | null) {
+    if (color != null) {
+      this.setAttribute("color", color);
+    } else {
+      this.removeAttribute("color");
+    }
+  }
+  get color() {
+    return this.getAttribute("color");
+  }
+
+  private _upgradeProperty(prop: any) {
+    if (this.hasOwnProperty(prop)) {
+      // @ts-ignore
+      let value = this[prop];
+      // @ts-ignore
+      delete this[prop];
+      // @ts-ignore
+      this[prop] = value;
+    }
+  }
+}