How do I find the values ​​of "prototype" in javascript?

I am using the following function to determine the values ​​that belong to the constructor of an object instead of the object itself.

function isAPrototypeValue(object, key ) {
  return !(object.constructor && object.constructor.prototype[key]);
}

      

        
        
        
      

    

it will work like this:

Array.prototype.base_value = 'base'
var array = new Array;
array.custom_value = 'custom'
alert( isAPrototypeValue( array, 'base_value' ) ) // true
alert( isAPrototypeValue( array, 'custom_value' ) ) // false 

      

        
        
        
      

    

But , when I started using inheritance:

function Base() {
  return this
};
Base.prototype.base_value = 'base';

function FirstSub() {
  return this
};
FirstSub.prototype = new Base();
FirstSub.prototype.first_value = 'first';

function SubB () {
  return this
};
SecondSub.prototype = new FirstSub();
SecondSub.prototype.second_value = 'second';

result = new SecondSub();

      

        
        
        
      

    

and I called

alert( result.constructor ) 

      

        
        
        
      

    

I would get Base instead of the expected SecondSub , which in itself is not a big problem, but ...

if i expanded the result like this:

result.custom_value = 'custom'
result.another_value = 'another'

      

        
        
        
      

    

I would expect to be able to distinguish between values ​​related to result or values ​​that belong to SecondSub, FirstSub, and Base ;

eg.

alert( isAPrototypeValue( result, 'custom_value' ) ) // false ( as expected )
alert( isAPrototypeValue( result, 'base_value' ) ) // true ( as expected )
alert( isAPrototypeValue( result, 'first_value' ) ) // true extend, but it is false
alert( isAPrototypeValue( result, 'second_value' ) ) // true extend, but it is false

      

        
        
        
      

    

How can I change isAPrototypeValue to output the expected results?