refactor objects, add optional chaining

1-js/04-object-basics/04-object-methods/article.md

@@ -233,98 +233,6 @@ The concept of run-time evaluated `this` has both pluses and minuses. On the one
 Here our position is not to judge whether this language design decision is good or bad. We'll understand how to work with it, how to get benefits and avoid problems.
 ```
 
-## Internals: Reference Type
-
-```warn header="In-depth language feature"
-This section covers an advanced topic, to understand certain edge-cases better.
-
-If you want to go on faster, it can be skipped or postponed.
-```
-
-An intricate method call can lose `this`, for instance:
-
-```js run
-let user = {
-  name: "John",
-  hi() { alert(this.name); },
-  bye() { alert("Bye"); }
-};
-
-user.hi(); // John (the simple call works)
-
-*!*
-// now let's call user.hi or user.bye depending on the name
-(user.name == "John" ? user.hi : user.bye)(); // Error!
-*/!*
-```
-
-On the last line there is a conditional operator that chooses either `user.hi` or `user.bye`. In this case the result is `user.hi`.
-
-Then the method is immediately called with parentheses `()`. But it doesn't work correctly!
-
-As you can see, the call results in an error, because the value of `"this"` inside the call becomes `undefined`.
-
-This works (object dot method):
-```js
-user.hi();
-```
-
-This doesn't (evaluated method):
-```js
-(user.name == "John" ? user.hi : user.bye)(); // Error!
-```
-
-Why? If we want to understand why it happens, let's get under the hood of how `obj.method()` call works.
-
-Looking closely, we may notice two operations in `obj.method()` statement:
-
-1. First, the dot `'.'` retrieves the property `obj.method`.
-2. Then parentheses `()` execute it.
-
-So, how does the information about `this` get passed from the first part to the second one?
-
-If we put these operations on separate lines, then `this` will be lost for sure:
-
-```js run
-let user = {
-  name: "John",
-  hi() { alert(this.name); }
-}
-
-*!*
-// split getting and calling the method in two lines
-let hi = user.hi;
-hi(); // Error, because this is undefined
-*/!*
-```
-
-Here `hi = user.hi` puts the function into the variable, and then on the last line it is completely standalone, and so there's no `this`.
-
-**To make `user.hi()` calls work, JavaScript uses a trick -- the dot `'.'` returns not a function, but a value of the special [Reference Type](https://tc39.github.io/ecma262/#sec-reference-specification-type).**
-
-The Reference Type is a "specification type". We can't explicitly use it, but it is used internally by the language.
-
-The value of Reference Type is a three-value combination `(base, name, strict)`, where:
-
-- `base` is the object.
-- `name` is the property name.
-- `strict` is true if `use strict` is in effect.
-
-The result of a property access `user.hi` is not a function, but a value of Reference Type. For `user.hi` in strict mode it is:
-
-```js
-// Reference Type value
-(user, "hi", true)
-```
-
-When parentheses `()` are called on the Reference Type, they receive the full information about the object and its method, and can set the right `this` (`=user` in this case).
-
-Reference type is a special "intermediary" internal type, with the purpose to pass information from dot `.` to calling parentheses `()`.
-
-Any other operation like assignment `hi = user.hi` discards the reference type as a whole, takes the value of `user.hi` (a function) and passes it on. So any further operation "loses" `this`.
-
-So, as the result, the value of `this` is only passed the right way if the function is called directly using a dot `obj.method()` or square brackets `obj['method']()` syntax (they do the same here). Later in this tutorial, we will learn various ways to solve this problem such as [func.bind()](/bind#solution-2-bind).
-
 ## Arrow functions have no "this"
 
 Arrow functions are special: they don't have their "own" `this`. If we reference `this` from such a function, it's taken from the outer "normal" function.