Getter and Setter methods for object properties in JavaScript: https://medium.com/@maurobringolf/javascript-data-encapsulation-and-property-getter-and-setter-methods-a59cbddf2ef4#.qimkogc2u

simple-getter-and-setter-property.js

//defining a normal property o.x using getters and setters
var o = {
  c: 1,
  get x() { return this.c; },
  set x(y) { this.c = y; }
}

o.x;      //1
o.x = 3;
o.x;      //3