refactor classes, add private, minor fixes

1-js/09-classes/03-class-inheritance/2-clock-class-extended/solution.view/extended-clock.js

@@ -0,0 +1,12 @@
+class ExtendedClock extends Clock {
+  constructor(options) {
+    super(options);
+    let { precision=1000 } = options;
+    this._precision = precision;
+  }
+
+  start() {
+    this._render();
+    this._timer = setInterval(() => this._render(), this._precision);
+  }
+};