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Ilya Kantor 2022-03-22 17:51:40 +03:00
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1-js/09-classes/03-static-properties-methods/article.md
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# Static properties and methods # Static properties and methods
We can also assign a method to the class function itself, not to its `"prototype"`. Such methods are called *static*. We can also assign a method to the class as a whole. Such methods are called *static*.
In a class, they are prepended by `static` keyword, like this: In a class declaration, they are prepended by `static` keyword, like this:
```js run ```js run
class User { class User {
@ -31,9 +31,11 @@ User.staticMethod(); // true
The value of `this` in `User.staticMethod()` call 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. Usually, static methods are used to implement functions that belong to the class as a whole, but not to any particular object of it.
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: For instance, we have `Article` objects and need a function to compare them.
A natural solution would be to add `Article.compare` static method:
```js run ```js run
class Article { class Article {
@ -63,9 +65,11 @@ articles.sort(Article.compare);
alert( articles[0].title ); // CSS alert( articles[0].title ); // CSS
``` ```
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. Here `Article.compare` method 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: Another example would be a so-called "factory" method.
Let's say, we need multiple ways to create an article:
1. Create by given parameters (`title`, `date` etc). 1. Create by given parameters (`title`, `date` etc).
2. Create an empty article with today's date. 2. Create an empty article with today's date.
@ -73,7 +77,7 @@ Another example would be a so-called "factory" method. Imagine, we need few ways
The first way can be implemented by the constructor. And for the second one we can make a static method of the class. The first way can be implemented by the constructor. And for the second one we can make a static method of the class.
Like `Article.createTodays()` here: Such as `Article.createTodays()` here:
```js run ```js run
class Article { class Article {
@ -101,7 +105,7 @@ Static methods are also used in database-related classes to search/save/remove e
```js ```js
// assuming Article is a special class for managing articles // assuming Article is a special class for managing articles
// static method to remove the article: // static method to remove the article by id:
Article.remove({id: 12345}); Article.remove({id: 12345});
``` ```