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improvement

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This commit is contained in:
Ilya Kantor 2018-01-14 20:14:22 +03:00
parent 634db3741c
commit c693192018
2 changed files with 13 additions and 19 deletions
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20
1-js/07-object-oriented-programming/10-class-inheritance/3-class-extend-object/solution.md
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@ -1,6 +1,6 @@
The answer has two parts. First, let's see why the latter code doesn't work.
The first, an easy one is that the inheriting class needs to call `super()` in the constructor. Otherwise `"this"` won't be "defined". The reason becomes obvious if we try to run it. An inheriting class constructor must call `super()`. Otherwise `"this"` won't be "defined".
So here's the fix: So here's the fix:
@ -37,7 +37,7 @@ alert( Rabbit.prototype.__proto__ === Object.prototype ); // (1) true
alert( Rabbit.__proto__ === Object ); // (2) true alert( Rabbit.__proto__ === Object ); // (2) true
``` ```
So we can access static methods of `Object` via `Rabbit`, like this: So `Rabbit` now provides access to static methods of `Object` via `Rabbit`, like this:
```js run ```js run
class Rabbit extends Object {} class Rabbit extends Object {}
@ -48,15 +48,16 @@ alert ( Rabbit.getOwnPropertyNames({a: 1, b: 2})); // a,b
*/!* */!*
``` ```
And if we don't use `extends`, then `class Rabbit` does not get the second reference. But if we don't have `extends Object`, then `Rabbit.__proto__` is not set to `Object`.
Please compare with it: Here's the demo:
```js run ```js run
class Rabbit {} class Rabbit {}
alert( Rabbit.prototype.__proto__ === Object.prototype ); // (1) true alert( Rabbit.prototype.__proto__ === Object.prototype ); // (1) true
alert( Rabbit.__proto__ === Object ); // (2) false (!) alert( Rabbit.__proto__ === Object ); // (2) false (!)
alert( Rabbit.__proto__ === Function.prototype ); // as any function by default
*!* *!*
// error, no such function in Rabbit // error, no such function in Rabbit
@ -64,14 +65,7 @@ alert ( Rabbit.getOwnPropertyNames({a: 1, b: 2})); // Error
*/!* */!*
``` ```
For the simple `class Rabbit`, the `Rabbit` function has the same prototype So `Rabbit` doesn't provide access to static methods of `Object` in that case.
```js run
class Rabbit {}
// instead of (2) that's correct for Rabbit (just like any function):
alert( Rabbit.__proto__ === Function.prototype );
```
By the way, `Function.prototype` has "generic" function methods, like `call`, `bind` etc. They are ultimately available in both cases, because for the built-in `Object` constructor, `Object.__proto__ === Function.prototype`. By the way, `Function.prototype` has "generic" function methods, like `call`, `bind` etc. They are ultimately available in both cases, because for the built-in `Object` constructor, `Object.__proto__ === Function.prototype`.

12
1-js/07-object-oriented-programming/10-class-inheritance/3-class-extend-object/task.md
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@ -4,9 +4,9 @@ importance: 5
# Class extends Object? # Class extends Object?
As we know, all objects normally inherit from `Object.prototype` and get access to "generic" object methods. As we know, all objects normally inherit from `Object.prototype` and get access to "generic" object methods like `hasOwnProperty` etc.
Like demonstrated here: For instance:
```js run ```js run
class Rabbit { class Rabbit {
@ -24,9 +24,11 @@ alert( rabbit.hasOwnProperty('name') ); // true
*/!* */!*
``` ```
So, is it correct to say that `"class Rabbit extends Object"` does exactly the same as `"class Rabbit"`, or not? But if we spell it out explicitly like `"class Rabbit extends Object"`, then the result would be different from a simple `"class Rabbit"`?
Will it work? What's the difference?
Here's an example of such code (it doesn't work -- why? fix it?):
```js ```js
class Rabbit extends Object { class Rabbit extends Object {
@ -39,5 +41,3 @@ let rabbit = new Rabbit("Rab");
alert( rabbit.hasOwnProperty('name') ); // true alert( rabbit.hasOwnProperty('name') ); // true
``` ```
If it won't please fix the code.