Member Assignment

var Oldsmobile = function(year, color) {
  // private members: 
  var allowed = ['red', 'black', 'tan'];
  var defaultColor = 'black';
  
  // manipulate instance initialization by accessing constructor methods: 
  Oldsmobile.addAllowed(allowed, 'blue');
  
  // privleged members: 
  this.color = allowed.find(_color => _color === color) ? color : defaultColor;
  this.speed = 0;
  this.drive = speed => this.speed = speed;
  this.year = year;
};

// public members: 
Oldsmobile.prototype.customPaintjob = function(_color){this.color = _color};

//constructor members: 
Oldsmobile.addAllowed = (colors, newColor) => colors.push(newColor);

var myAntiqueCar = new Oldsmobile(1904, 'blue');
myAntiqueCar.drive(10);
myAntiqueCar.customPaintjob('orange');
myAntiqueCar;

// source: https://crockford.com/javascript/private.html