refactor classes, add private, minor fixes

1-js/09-classes/03-class-inheritance/3-class-extend-object/task.md

@@ -0,0 +1,43 @@
+importance: 5
+
+---
+
+# Class extends Object?
+
+As we know, all objects normally inherit from `Object.prototype` and get access to "generic" object methods like `hasOwnProperty` etc.
+
+For instance:
+
+```js run
+class Rabbit {
+  constructor(name) {
+    this.name = name;
+  }
+}
+
+let rabbit = new Rabbit("Rab");
+
+*!*
+// hasOwnProperty method is from Object.prototype
+// rabbit.__proto__ === Object.prototype
+alert( rabbit.hasOwnProperty('name') ); // true
+*/!*
+```
+
+But if we spell it out explicitly like `"class Rabbit extends Object"`, then the result would be different from a simple `"class Rabbit"`?
+
+What's the difference?
+
+Here's an example of such code (it doesn't work -- why? fix it?):
+
+```js
+class Rabbit extends Object {
+  constructor(name) {
+    this.name = name;
+  }
+}
+
+let rabbit = new Rabbit("Rab");
+
+alert( rabbit.hasOwnProperty('name') ); // true
+```