Is there a static version of `instanceof`?

January 17, 2024

Is there a static equivalent of instanceof? I.E., rather than:
obj1 instanceof Type
something like:
TypeA instanceof TypeB?

I couldn’t find anything on the matter, so I hacked together this:

function InstanceOf(type,parent) {
    do{ if(type === parent) return true;}
    while(type = Object.getPrototypeOf(type));
    return false;
}
//...
Instanceof(ChildClass, ParentClass); // = boolean

But I feel like there’s a better/more native way to do this, but again, can’t find anything on it.

Is there a better/standard way do check static class inheritance? Or is my hack about the best it’s gonna get?

>Solution :

You can use isPrototypeOf.

class A {}
class B extends A {}
class C extends B {}
const InstanceOf = (type, parent) => type === parent || parent.prototype.isPrototypeOf(type.prototype);
console.log(InstanceOf(B, A));
console.log(InstanceOf(A, A));
console.log(InstanceOf(C, A));
console.log(InstanceOf(C, B));
console.log(InstanceOf(B, C));