refactor classes, add private, minor fixes

1-js/09-classes/03-class-inheritance/1-class-constructor-error/solution.md

@@ -0,0 +1,27 @@
+That's because the child constructor must call `super()`.
+
+Here's the corrected code:
+
+```js run
+class Animal {
+
+  constructor(name) {
+    this.name = name;
+  }
+
+}
+
+class Rabbit extends Animal {
+  constructor(name) {  
+    *!*
+    super(name);
+    */!*
+    this.created = Date.now();
+  }
+}
+
+*!*
+let rabbit = new Rabbit("White Rabbit"); // ok now
+*/!*
+alert(rabbit.name); // White Rabbit
+```