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

pseudo-strict-encapsulation.js

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

//Make the property o.__c non-enumerable
Object.defineProperty(o, '__c', { enumerable: false });

//Object.keys and for...in loop skip x.c now
Object.keys(o);   //["x"]

//The property can still be accessed using its name
o.__c = 2;
o.__c;            //2