function X() {}
X.prototype.getValue = function() {
  return this.value;
};

function Y() {
  this.value = 42;
}
Y.prototype = Object.create(X.prototype);
Y.prototype.constructor = Y;

var y = new Y();
console.log(y.getValue());

function A() {}
A.prototype.value = 1;

function B() {}
B.prototype = new A();

B.prototype.value = 2;

var b = new B();
console.log(b.value);

let obj = { a: 1 };
let proto = { b: 2 };

Object.setPrototypeOf(obj, proto);

for (let key in obj) {
  console.log(key);
}

let obj = { a: 1 };
Object.freeze(obj);

console.log(Object.isFrozen(obj));
console.log(obj.a = 2);
console.log(obj.a);

let obj = {};
Object.defineProperty(obj, 'a', {
  value: 1,
  enumerable: true
});

let clone = Object.create(
  Object.getPrototypeOf(obj),
  Object.getOwnPropertyDescriptors(obj)
);

console.log(clone.a);
console.log(clone.hasOwnProperty('a'));

let proto = { a: 1 };
let obj = Object.create(proto);

Object.defineProperty(obj, 'a', {
  value: 2,
  writable: false,
  enumerable: true,
  configurable: false
});

console.log(obj.a);
proto.a = 3;
console.log(obj.a);