refactor classes, add private, minor fixes

1-js/09-classes/01-class-patterns/1-inheritance-error-assign/solution.md

@@ -0,0 +1,46 @@
+Here's the line with the error:
+
+```js
+Rabbit.prototype = Animal.prototype;
+```
+
+Here `Rabbit.prototype` and `Animal.prototype` become the same object. So methods of both classes become mixed in that object.
+
+As a result, `Rabbit.prototype.walk` overwrites `Animal.prototype.walk`, so all animals start to bounce:
+
+```js run
+function Animal(name) {
+  this.name = name;
+}
+
+Animal.prototype.walk = function() {
+  alert(this.name + ' walks');
+};
+
+function Rabbit(name) {
+  this.name = name;
+}
+
+*!*
+Rabbit.prototype = Animal.prototype;
+*/!*
+
+Rabbit.prototype.walk = function() {
+  alert(this.name + " bounces!");
+};
+
+*!*
+let animal = new Animal("pig");
+animal.walk(); // pig bounces!
+*/!*
+```
+
+The correct variant would be:
+
+```js
+Rabbit.prototype.__proto__ = Animal.prototype;
+// or like this:
+Rabbit.prototype = Object.create(Animal.prototype);
+```
+
+That makes prototypes separate, each of them stores methods of the corresponding class, but `Rabbit.prototype` inherits from `Animal.prototype`.