gistfile1.js

var PublicShape = function() {
  // public members
  this.width = 50;
  this.height = 50;
};

PublicShape.prototype.getWidth = function() {
  // public method with priveledged access to the private members
  return this.width;
}

var publicShape = new PublicShape();

console.log( publicShape.width ); // will output 50
console.log( publicShape.getWidth() ); // will output 50

var PrivateShape = function() {
  // private members
  var width = 100
    , height = 100;
  // i am public and now a property on the global object 
  // because I did not declare myself using the keyword var
  length = 300;
  // public method with priveledged access to the private members
  this.getWidth = function() {
    return width;
  };
};


var privateShape = new PrivateShape();

console.log( privateShape.width ); // will output undefined
console.log( privateShape.getWidth() ); // will output 50

console.log( privateShape.length ) // will output undefined
console.log( window.length ) // will output 300