Check if object is a 'direct instance' of a class

Question

I have two classes:

class Bar extends Foo { // Foo isn\'t relevant
  constructor(value) {
    if (!(value instanceof Foo)) throw \"InvalidArgumentException:          


        

Answer 1

You should test if value's internal [[Prototype]] is exactly Foo.prototype. You can get the internal [[Prototype]] with Object.getPrototypeOf :

if ( Object.getPrototypeOf( value ) !== Foo.prototype )
   throw "InvalidArgumentException: (...)";