Check if a constructor inherits another in ES6

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Because of the way instanceof works, you should be able to do

A.prototype instanceof B

But this would only test inheritance, you should have to compare A === B to test for self-reference:

A === B || A.prototype instanceof B

Babel example:

class A {}
class B extends A {}
class C extends B {}

console.log(C === C) // true
console.log(C.prototype instanceof B) // true
console.log(C.prototype instanceof A) // true

instanceof is basically implemented as follows:

function instanceof(obj, Constr) {
  var proto;
  while ((proto = Object.getProtoypeOf(obj)) {
    if (proto === Constr.prototype) {
      return true;
    }
  }
  return false;
}

It iterates over the prototype chain of the object and checks whether any of the prototypes equals the constructors prototype property.

So almost like what you were doing, but internally.

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