minor

1-js/09-classes/02-class-inheritance/article.md

@@ -17,7 +17,7 @@ class Animal {
   }
   stop() {
     this.speed = 0;
-    alert(`${this.name} stopped.`);
+    alert(`${this.name} stands still.`);
   }
 }
 
@@ -65,7 +65,7 @@ class Animal {
   }
   stop() {
     this.speed = 0;
-    alert(`${this.name} stopped.`);
+    alert(`${this.name} stands still.`);
   }
 }
 
@@ -155,7 +155,7 @@ class Animal {
 
   stop() {
     this.speed = 0;
-    alert(`${this.name} stopped.`);
+    alert(`${this.name} stands still.`);
   }
 
 }
@@ -176,7 +176,7 @@ class Rabbit extends Animal {
 let rabbit = new Rabbit("White Rabbit");
 
 rabbit.run(5); // White Rabbit runs with speed 5.
-rabbit.stop(); // White Rabbit stopped. White rabbit hides!
+rabbit.stop(); // White Rabbit stands still. White rabbit hides!
 ```
 
 Now `Rabbit` has the `stop` method that calls the parent `super.stop()` in the process.
@@ -265,12 +265,12 @@ In JavaScript, there's a distinction between a "constructor function of an inher
 
 The difference is:
 
-- When a normal constructor runs, it creates an empty object as `this` and continues with it.
+- When a normal constructor runs, it creates an empty object and assigns it to `this`.
-- But when a derived constructor runs, it doesn't do it. It expects the parent constructor to do this job.
+- But when a derived constructor runs, it doesn't do this. It expects the parent constructor to do this job.
 
-So if we're making a constructor of our own, then we must call `super`, because otherwise the object with `this` reference to it won't be created. And we'll get an error.
+So if we're making a constructor of our own, then we must call `super`, because otherwise the object for `this` won't be created. And we'll get an error.
 
-For `Rabbit` to work, we need to call `super()` before using `this`, like here:
+For `Rabbit` constructor to work, it needs to call `super()` before using `this`, like here:
 
 ```js run
 class Animal {
@@ -306,16 +306,24 @@ alert(rabbit.earLength); // 10
 
 ## Super: internals, [[HomeObject]]
 
+```warn header="Advanced information"
+If you're reading the tutorial for the first time - this section may be skipped.
+
+It's about the internal mechanisms behind inheritance and `super`.
+```
+
 Let's get a little deeper under the hood of `super`. We'll see some interesting things by the way.
 
 First to say, from all that we've learned till now, it's impossible for `super` to work at all!
 
-Yeah, indeed, let's ask ourselves, how it could technically work? When an object method runs, it gets the current object as `this`. If we call `super.method()` then, it needs to retrieve the `method` from the prototype of the current object.
+Yeah, indeed, let's ask ourselves, how it should technically work? When an object method runs, it gets the current object as `this`. If we call `super.method()` then, the engine needs to get the `method` from the prototype of the current object. But how?
 
 The task may seem simple, but it isn't. The engine knows the current object `this`, so it could get the parent `method` as `this.__proto__.method`. Unfortunately, such a "naive" solution won't work.
 
 Let's demonstrate the problem. Without classes, using plain objects for the sake of simplicity.
 
+You may skip this part and go below to the `[[HomeObject]]` subsection if you don't want to know the details. That won't harm. Or read on if you're interested in understanding things in-depth.
+
 In the example below, `rabbit.__proto__ = animal`. Now let's try: in `rabbit.eat()` we'll call `animal.eat()`, using `this.__proto__`:
 
 ```js run
@@ -459,7 +467,7 @@ The very existance of `[[HomeObject]]` violates that principle, because methods
 
 The only place in the language where `[[HomeObject]]` is used -- is `super`. So, if a method does not use `super`, then we can still consider it free and copy between objects. But with `super` things may go wrong.
 
-Here's the demo of a wrong `super` call:
+Here's the demo of a wrong `super` result after copying:
 
 ```js run
 let animal = {
@@ -468,6 +476,7 @@ let animal = {
   }
 };
 
+// rabbit inherits from animal
 let rabbit = {
   __proto__: animal,
   sayHi() {
@@ -481,6 +490,7 @@ let plant = {
   }
 };
 
+// tree inherits from plant
 let tree = {
   __proto__: plant,
 *!*
@@ -497,9 +507,11 @@ A call to `tree.sayHi()` shows "I'm an animal". Definitevely wrong.
 
 The reason is simple:
 - In the line `(*)`, the method `tree.sayHi` was copied from `rabbit`. Maybe we just wanted to avoid code duplication?
-- So its `[[HomeObject]]` is `rabbit`, as it was created in `rabbit`. There's no way to change `[[HomeObject]]`.
+- Its `[[HomeObject]]` is `rabbit`, as it was created in `rabbit`. There's no way to change `[[HomeObject]]`.
 - The code of `tree.sayHi()` has `super.sayHi()` inside. It goes up from `rabbit` and takes the method from `animal`.
 
+Here's the diagram of what happens:
+
 ![](super-homeobject-wrong.svg)
 
 ### Methods, not function properties

1-js/09-classes/03-static-properties-methods/article.md

@@ -1,9 +1,9 @@
 
 # Static properties and methods
 
-We can also assign a method to the class function, not to its `"prototype"`. Such methods are called *static*.
+We can also assign a method to the class function itself, not to its `"prototype"`. Such methods are called *static*.
 
-An example:
+In a class, they are prepended by `static` keyword, like this:
 
 ```js run
 class User {
@@ -17,7 +17,7 @@ class User {
 User.staticMethod(); // true
 ```
 
-That actually does the same as assigning it as a property:
+That actually does the same as assigning it as a property directly:
 
 ```js
 class User() { }
@@ -27,11 +27,11 @@ User.staticMethod = function() {
 };
 ```
 
-The value of `this` inside `User.staticMethod()` is the class constructor `User` itself (the "object before dot" rule).
+The value of `this` in `User.staticMethod()` call is the class constructor `User` itself (the "object before dot" rule).
 
 Usually, static methods are used to implement functions that belong to the class, but not to any particular object of it.
 
-For instance, we have `Article` objects and need a function to compare them. The natural choice would be `Article.compare`, like this:
+For instance, we have `Article` objects and need a function to compare them. A natural solution would be to add `Article.compare` method, like this:
 
 ```js run
 class Article {
@@ -61,13 +61,13 @@ articles.sort(Article.compare);
 alert( articles[0].title ); // CSS
 ```
 
-Here `Article.compare` stands "over" the articles, as a means to compare them. It's not a method of an article, but rather of the whole class.
+Here `Article.compare` stands "above" articles, as a means to compare them. It's not a method of an article, but rather of the whole class.
 
 Another example would be a so-called "factory" method. Imagine, we need few ways to create an article:
 
 1. Create by given parameters (`title`, `date` etc).
 2. Create an empty article with today's date.
-3. ...
+3. ...or else somehow.
 
 The first way can be implemented by the constructor. And for the second one we can make a static method of the class.
 
@@ -107,7 +107,7 @@ Article.remove({id: 12345});
 
 [recent browser=Chrome]
 
-Static properties are also possible, just like regular class properties:
+Static properties are also possible, they look like regular class properties, but prepended by `static`:
 
 ```js run
 class Article {
@@ -123,9 +123,9 @@ That is the same as a direct assignment to `Article`:
 Article.publisher = "Ilya Kantor";
 ```
 
-## Statics and inheritance
+## Inheritance of static methods
 
-Statics are inherited, we can access `Parent.method` as `Child.method`.
+Static methods are inherited.
 
 For instance, `Animal.compare` in the code below is inherited and accessible as `Rabbit.compare`:
 
@@ -169,36 +169,39 @@ rabbits.sort(Rabbit.compare);
 rabbits[0].run(); // Black Rabbit runs with speed 5.
 ```
 
-Now we can call `Rabbit.compare` assuming that the inherited `Animal.compare` will be called.
+Now when we can call `Rabbit.compare`, the inherited `Animal.compare` will be called.
 
 How does it work? Again, using prototypes. As you might have already guessed, `extends` gives `Rabbit` the `[[Prototype]]` reference to `Animal`.
 
-
 ![](animal-rabbit-static.svg)
 
-So, `Rabbit` function now inherits from `Animal` function. And `Animal` function normally has `[[Prototype]]` referencing `Function.prototype`, because it doesn't `extend` anything.
+So, `Rabbit extends Animal` creates two `[[Prototype]]` references:
 
-Here, let's check that:
+1. `Rabbit` function prototypally inherits from `Animal` function.
+2. `Rabbit.prototype` prototypally inherits from `Animal.prototype`.
+
+As the result, inheritance works both for regular and static methods.
+
+Here, let's check that by code:
 
 ```js run
 class Animal {}
 class Rabbit extends Animal {}
 
-// for static properties and methods
+// for statics
 alert(Rabbit.__proto__ === Animal); // true
 
-// the next step up leads to Function.prototype
+// for regular methods
-alert(Animal.__proto__ === Function.prototype); // true
-
-// the "normal" prototype chain for object methods
 alert(Rabbit.prototype.__proto__ === Animal.prototype);
 ```
 
-This way `Rabbit` has access to all static methods of `Animal`.
-
 ## Summary
 
-Static methods are used for the functionality that doesn't relate to a concrete class instance, doesn't require an instance to exist, but rather belongs to the class as a whole, like `Article.compare` -- a generic method to compare two articles.
+Static methods are used for the functionality that belongs to the class "as a whole", doesn't relate to a concrete class instance.
+
+For example, a method for comparison `Article.compare(article1, article2)` or a factory method `Article.createTodays()`.
+
+They are labeled by the word `static` in class declaration.
 
 Static properties are used when we'd like to store class-level data, also not bound to an instance.
 
@@ -214,7 +217,7 @@ class MyClass {
 }
 ```
 
-That's technically the same as assigning to the class itself:
+Technically, static declaration is the same as assigning to the class itself:
 
 ```js
 MyClass.property = ...
@@ -223,4 +226,4 @@ MyClass.method = ...
 
 Static properties are inherited.
 
-Technically, for `class B extends A` the prototype of the class `B` itself points to `A`: `B.[[Prototype]] = A`. So if a field is not found in `B`, the search continues in `A`.
+For `class B extends A` the prototype of the class `B` itself points to `A`: `B.[[Prototype]] = A`. So if a field is not found in `B`, the search continues in `A`.