Access static mathod before using »super« - oop

Question

there is this class hierarchy:
class A {
constructor (obj) {
this.obj = obj
}
}
class B extends A {
static createObj () {
return {from: 'B'};
}
constructor () {
const obj = B.createObj();
super(obj);
}
}
I would like to extend this such that:
class C extends B {
static createObj () {
return { from: 'C' };
}
}
//such that:
console.log(new C().obj.from) // 'C'
BUT therefore I need to change const obj = B.createObj() to something like: const obj = Object.getPrototypeOf(this).constructor.createObj();, what is throwing this error:
ReferenceError: Must call super constructor in derived class before accessing 'this' or returning from derived constructor
So basically I would like to override a method that creates an object to be used within the super() call. Since this cannot be used before that, I chose to use a static method. Is there any way to reference the static method, without using this and without overriding the constructor as well?

Answer 1

If you really want your this.obj=obj to be done only in class A for some reason, then I would do:
class A {
constructor(obj) {
this.obj = obj
}
}
class B extends A {
static createObj() {
return { from: 'B' };
}
constructor(obj) {
if (!obj) obj = B.createObj();
super(obj);
}
}
class C extends B {
static createObj() {
return { from: 'C' };
}
constructor(obj) {
if (!obj) obj = C.createObj();
super(obj);
}
}
console.log(new C().obj.from)
Output:
"C"
But in my opinion the best OOP approach would be this:
class A {
constructor(obj) {
this.obj = obj
}
}
class B extends A {
static createObj() {
return { from: 'B' };
}
constructor(obj) {
super(obj);
this.obj = B.createObj();
}
}
class C extends B {
static createObj() {
return { from: 'C' };
}
constructor(obj) {
super(obj);
this.obj = C.createObj();
}
}
console.log(new C().obj.from)
Output:
"C"
The 2nd approach allows to satisfy the pattern "call super before doing anything else" that can prevent bugs.
It's up to you to chose which one better suits your needs, but both prints "C" without requiring Object.getPrototypeOf(this).constructor.createObj()