design_pattern4.js

function MacBook() {
  this.cost = function () { return 997; }
  this.screenSize = function () { return 11.6; };
}

// Decorator 1
function Memory ( macbook ) {
  var v = macbook.cost();
  macbook.cost = function() {
    return v + 75;
  };
}

// Decorator 2
function Engraving ( macbook ) {
  var v = macbook.cost();
  macbook.cost = function() {
    return v + 200;
  };
}

// Decorator 3
function Insurance ( macbook ) {
  var v = macbook.cost();
  macbook.cost = function() {
    return v + 250;
  };
}

var mb = new MacBook();
Memory( mb );
Engraving( mb );
Insurance( mb );

console.log(mb.cost()); // 1522
console.log(mb.screenSize()); 11.6