What is the reason for the DOMException constructor deriving directly from Function.prototype, while the DOMException prototype derives directly from Error.prototype?

Question

What is the reason for the DOMException constructor deriving directly from Function.prototype, while the DOMException prototype derives directly from Error.prototype?

Why is DOMException different from AggregateError, EvalError, and others in terms of its prototype chain?

Both of these statements are true:

Object.getPrototypeOf(DOMException) === Function.prototype
Object.getPrototypeOf(DOMException.prototype) === Error.prototype

I once believed that the following rule always applied:

If

X and Y are constructor functions, and
Y is not the Object() constructor, and
X.prototype has Y.prototype as its [[Prototype]] object Then
X has Y as its [[Prototype]] object

For example, this rule holds for pairs like:

HTMLElement, Element
AggregateError, Error
AsyncFunction, Function
Node, EventTarget
Element, Node
RTCError, DOMException

The only exception I know of is when X = DOMException and Y = Error.

Is there a specific reason why the DOMException constructor cannot have the Error constructor as its [[Prototype]]?

javascript prototype-chain domexception

Answer 1

Answer №1

If an object's prototype is another object's prototype,
Then the first object inherits from the second object

No, this statement is not universally applicable. While it has become common post-ES6 with the introduction of class inheritance, many libraries still follow the old pattern where constructor functions inherit directly from Function.prototype. However, for most built-in classes such as native ECMAScript and DOM classes, this generalization holds true. The Error hierarchy, for example, consciously switched to this model in ES6.

Web APIs adhere to a specific pattern for interfaces outlined in the Web IDL specification. This standardizes how constructors and prototypes should be linked based on interface inheritance.

One interesting exception is the Window constructor which inherits from EventTarget while its prototype inherits from WindowProperties (which itself inherits from EventTarget.prototype).

Is there a reason why the DOMException constructor doesn't inherit from the Error constructor?

No, but possible reasons include historical factors, compatibility concerns, or delays in browser implementations. Web IDL explicitly states this as an exceptional case where DOMException does not inherit from Error but still shares the same prototype internal slot. This was clarified in recent discussions and updates to align with implementation realities.

Answer 2

If an object's prototype is another object's prototype,
Then the first object inherits from the second object

No, this statement is not universally applicable. While it has become common post-ES6 with the introduction of class inheritance, many libraries still follow the old pattern where constructor functions inherit directly from Function.prototype. However, for most built-in classes such as native ECMAScript and DOM classes, this generalization holds true. The Error hierarchy, for example, consciously switched to this model in ES6.

Web APIs adhere to a specific pattern for interfaces outlined in the Web IDL specification. This standardizes how constructors and prototypes should be linked based on interface inheritance.

One interesting exception is the Window constructor which inherits from EventTarget while its prototype inherits from WindowProperties (which itself inherits from EventTarget.prototype).

Is there a reason why the DOMException constructor doesn't inherit from the Error constructor?

No, but possible reasons include historical factors, compatibility concerns, or delays in browser implementations. Web IDL explicitly states this as an exceptional case where DOMException does not inherit from Error but still shares the same prototype internal slot. This was clarified in recent discussions and updates to align with implementation realities.

Answer 3

Answer №2

Every constructor is derived from the Function function because it essentially functions as a function and has no direct connection to its prototype:

class Example{

}

console.log(Object.getPrototypeOf(Example.constructor).constructor.name);

function Example2(){

}

console.log(Object.getPrototypeOf(Example2.constructor).constructor.name);

console.log(Object.getPrototypeOf(Set.constructor).constructor.name);

Answer 4

Every constructor is derived from the Function function because it essentially functions as a function and has no direct connection to its prototype:

class Example{

}

console.log(Object.getPrototypeOf(Example.constructor).constructor.name);

function Example2(){

}

console.log(Object.getPrototypeOf(Example2.constructor).constructor.name);

console.log(Object.getPrototypeOf(Set.constructor).constructor.name);

What is the reason for the DOMException constructor deriving directly from Function.prototype, while the DOMException prototype derives directly from Error.prototype?

Answer №1

Answer №2

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