What is the reason that other classes in JavaScript do not inherit the static methods of the Object class?

Question

What is the reason that other classes in JavaScript do not inherit the static methods of the Object class?

When working with JavaScript, it's interesting to note that creating a class with a static method allows you to call that method using the subclass name as well, since static methods are inherited.

The Object class, which serves as the superclass for all classes in JavaScript, offers many static methods. However, despite this widespread inheritance, none of those methods can be called using any subclass names.

Click here for more information on static methods within the Object class.

Some have suggested explicitly using 'extend' Object, but this seems unnecessary given that Object is already the implicit superclass for every class in JavaScript. This can be seen through examples like the .toString() method, which is present in every object from every class and is inherited from the Object class without needing to explicitly write 'extends Object'.

It's worth questioning why non-static methods are automatically inherited while static methods are not. Consider the following sample code:

class Test {
  constructor() {}
}

const test = new Test();
console.log(test.toString()); // works, inherited from Object class
console.log(Test.<any static method of Object>)); // doesn't work

javascript inheritance static

Answer 1

Answer №1

Back in 2012, during the development of ES6, a deliberate decision was made regarding inheritance. This decision can be traced back to the meeting notes on "Maxmin class semantics": view the notes here.

Mark S. Miller: raised concerns about inheriting methods like Object.create and Object.getOwnPropertyDescriptor

Dave Herman: pointed out potential issues with adding methods to Object

[…]

Allen Wirfs-Brock: explained that opting into this behavior would involve using class Point extends Object

[…]

Yehuda Katz: highlighted the importance of avoiding pollution from static methods when dealing with subclassing

The decision not to inherit certain properties from Object was deemed beneficial. In ES5, not inheriting class objects was considered but ultimately dismissed due to complexity surrounding dynamic usage of static methods on subclasses. At the time, there was no explicit static modifier for defining methods, complicating the process.

The static methods of Object were designed to be non-dynamic and strictly utilitarian, void of receiver (this) involvement. The intent was never for them to be called on subclasses. Object serves as a basic toolset for object manipulation, separate from class inheritance necessities.

Simplicity was prioritized in cases where classes do not extend another class (including Object) - constructors are streamlined without the need for super(). This focus on usability reflects common needs, making inheritance from Object an optional feature for class objects.

This design choice aligns with the precedent set by other built-in classes such as Function.prototype, Array.prototype, and Error.prototype, which inherit from Object.prototype while maintaining constructor independence from Object.

Early tutorial materials also support this approach, emphasizing the distinction between extending and not extending classes for more intuitive class construction.

Answer 2

Back in 2012, during the development of ES6, a deliberate decision was made regarding inheritance. This decision can be traced back to the meeting notes on "Maxmin class semantics": view the notes here.

Mark S. Miller: raised concerns about inheriting methods like Object.create and Object.getOwnPropertyDescriptor

Dave Herman: pointed out potential issues with adding methods to Object

[…]

Allen Wirfs-Brock: explained that opting into this behavior would involve using class Point extends Object

[…]

Yehuda Katz: highlighted the importance of avoiding pollution from static methods when dealing with subclassing

The decision not to inherit certain properties from Object was deemed beneficial. In ES5, not inheriting class objects was considered but ultimately dismissed due to complexity surrounding dynamic usage of static methods on subclasses. At the time, there was no explicit static modifier for defining methods, complicating the process.

The static methods of Object were designed to be non-dynamic and strictly utilitarian, void of receiver (this) involvement. The intent was never for them to be called on subclasses. Object serves as a basic toolset for object manipulation, separate from class inheritance necessities.

Simplicity was prioritized in cases where classes do not extend another class (including Object) - constructors are streamlined without the need for super(). This focus on usability reflects common needs, making inheritance from Object an optional feature for class objects.

This design choice aligns with the precedent set by other built-in classes such as Function.prototype, Array.prototype, and Error.prototype, which inherit from Object.prototype while maintaining constructor independence from Object.

Early tutorial materials also support this approach, emphasizing the distinction between extending and not extending classes for more intuitive class construction.

Answer 3

Answer №2

It's important to note that initially, JavaScript did not include classes. When the concept was introduced, it was essentially added as a shortcut for constructor functions, which are instances of Function.

When dealing with static properties and methods, what really matters is the prototype of the constructor function itself (not the prototype of instances created from that constructor). For a class defined without extending another class using extend, the prototype of the constructor function is actually Function.prototype, not Object.prototype.

class A {}
class B extends Object {}

console.log(Object.getPrototypeOf(A) === Function.prototype); // true
console.log(Object.getPrototypeOf(A) === Object); // false
console.log(Object.getPrototypeOf(B) === Object); // true

Function.prototype may not have properties like keys or entries, but it does possess properties like apply, call, and bind, allowing you to call these functions on any function. Therefore, in your case, Test.apply does have a value.

If Test.entries were to inherit from Object.entries, then Function.entries would also do the same, creating potential confusion.

Answer 4

It's important to note that initially, JavaScript did not include classes. When the concept was introduced, it was essentially added as a shortcut for constructor functions, which are instances of Function.

When dealing with static properties and methods, what really matters is the prototype of the constructor function itself (not the prototype of instances created from that constructor). For a class defined without extending another class using extend, the prototype of the constructor function is actually Function.prototype, not Object.prototype.

class A {}
class B extends Object {}

console.log(Object.getPrototypeOf(A) === Function.prototype); // true
console.log(Object.getPrototypeOf(A) === Object); // false
console.log(Object.getPrototypeOf(B) === Object); // true

Function.prototype may not have properties like keys or entries, but it does possess properties like apply, call, and bind, allowing you to call these functions on any function. Therefore, in your case, Test.apply does have a value.

If Test.entries were to inherit from Object.entries, then Function.entries would also do the same, creating potential confusion.

Answer 5

Answer №3

The original poster inquired about the necessity of extending Test with Object to enable the use of static methods.
In JavaScript, classes were introduced as an ES6 feature, surpassing the previous use of prototypes only.
To utilize JS classes, explicit extension from a base class is mandatory.
Failure to do so results in the instances of the class being implicitly extended from Object using Object.prototype

Therefore, static methods will not be accessible.

To illustrate this concept:

class Test extends Object{

}

console.log(Test.values({key:'value'}));

// Without a base class
class Test2{
    test = 'test'
}

// Confirming usage of Object.prototype
console.log(new Test2 instanceof Object);
console.log(new Test2().hasOwnProperty('test'));

// Unfortunately, static methods are unavailable   
console.log(Test2.values({key:'value'}));

Answer 6

The original poster inquired about the necessity of extending Test with Object to enable the use of static methods.
In JavaScript, classes were introduced as an ES6 feature, surpassing the previous use of prototypes only.
To utilize JS classes, explicit extension from a base class is mandatory.
Failure to do so results in the instances of the class being implicitly extended from Object using Object.prototype

Therefore, static methods will not be accessible.

To illustrate this concept:

class Test extends Object{

}

console.log(Test.values({key:'value'}));

// Without a base class
class Test2{
    test = 'test'
}

// Confirming usage of Object.prototype
console.log(new Test2 instanceof Object);
console.log(new Test2().hasOwnProperty('test'));

// Unfortunately, static methods are unavailable   
console.log(Test2.values({key:'value'}));

What is the reason that other classes in JavaScript do not inherit the static methods of the Object class?

Answer №1

Answer №2

Answer №3

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