How to check if a class B extends A during runtime

Question

In TypeScript/Javscript, how do I check if class B extends class A

class A {
  ...
}

class B extends A {
  ...
}

assert(B extends A) // How to do something like this?

---

Answer:

Couple of ways to do this. Thanks to @Daniel and @AviatorX

B.prototype instanceof A        // true
Object.getPrototypeOf(B) === A  // true
Reflect.getPrototypeOf(B) === A // true

Not sure whats the most TypeScript idiomatic way to do it or if there are any missing edge cases but worked for my use case

Answer 1

You can use the instanceof to check if the constructor prototype is an instance of A:

export class A {
}

export class B extends A {
}

console.log(B.prototype instanceof A);

Outputs true for me.