QUESTION: Что такое static в классах?

The static keyword in JavaScript classes opens up possibilities for creating static properties and methods that belong not to a specific object instance, but to the class as a whole. Declaring a static method looks like static method() {}, and a static field is defined via a construction like static property = value. The main difference between static members and regular ones lies in the way they are called: they are accessed exclusively through the class name, for example ClassName.method(), rather than through a created object instance.

Moreover, trying to call a static method or read a static property via a variable storing a class instance will result in an error, since these entities simply do not fall into the object's prototype chain. Memory for static members is allocated once when the class is loaded into memory, and they exist regardless of whether at least one application or instance of this class has been created.

In practice, static methods and properties are most often used to implement various utility functions, auxiliary algorithms, factory methods for creating objects, as well as to store constants or general state that should be uniform for all future instances of a given class. For example, a Database class can contain a static Database.connect() method that returns a single database connection following the Singleton pattern.

Using static allows you to logically isolate logic that does not depend on the data of a specific object, making the code cleaner, more structured, and professional. Developers can easily group auxiliary tools right inside business classes without creating separate files with scattered functions for this purpose.