print(aa instanceof Child);
print(aa instanceof Parent);

to the end of that code, and it prints

true
true

“A instanceof F” tests if F.prototype appears in the prototype chain for A, which it does in this instance.


var c= new Child();
if (c instanceof Parent)
// clever processing here


If you’re looking for a general purpose helper for inheritence you might consider something like the following:


Function.prototype.extendsClass= function( base )
{
this.prototype= new base();
this.prototype.constructor= this;
}


Then you can write your initialisers like the following:


function Parent( name )
{
this.name= name;
}
Parent.prototype.sharedArray= [];


function Child( first, last )
{
Parent.call( this, first + " " + last );
}
Child.extendsClass( Parent );


Then you can fully use the instanceof operator.

Just a thought…