Question

Is there a difference between Object.getPrototypeOf(obj) and obj.constructor.prototype? Or are these two referencing the same thing?

Answer 1

NO

It returns the internal [[Prototype]] value.

For example:

var o = Object.create(null);
Object.getPrototypeOf(o); // null
o.constructor.prototype; // error

var p = {};
var o = Object.create(p);
Object.getPrototypeOf(o); // p
o.constructor.prototype; // Object.prototype

o.constructor.prototype only works with objects created through new ConstructorFunction or where you have manually set the Prototype.prototype.constructor === Prototype relationship.