instantiateing prototype and __proto__ parent class

function Class(){}
var instance1 = new Class();

var instance2 = {};

instance2.constructor = Class;
instance2.__proto__ = Class.prototype;

//rototype when instantiate, you already set prototype's ___proto__ to the function's constructor

Class.apply(instance2);

instance[1|2].constructor == Class
instance[1|2].__proto__ = Class.prototype
instance[1|2] instanceof Class = true

//What does a function's prototype do?

function Circle(radius) {
 this.radius = radius;
}

Circle.prototype.area = function() {
  return this.radius * this.radius * Math.Pi;
}

var instance = new Circle(5);
instance.area() ==> 78.5275

instance.constructor == Circle
instance.__proto__ == Circle.prototype
instance instanceof Circle = true