design_pattern2.js

// A constructor for defining new cars
function Car (options) {
  // some defaults
  this.doors = options.doors || 4;
  this.state = options.state || "brand new";
  this.color = options.color || "silver";  
}

// A constructor for defining new trucks

function Truck (options) {
  // some defaults
  this.state = options.state || "used";
  this.wheelSize = options.wheelSize || "large";
  this.color = options.color || "blue";  
}

// Define a skeleton vehicle factory
function VehicleFactory() {}

// Default vehicleClass is Car
VehicleFactory.prototype.vehicleClass = Car;

// Factory method for creating new Vehicle instances
VehicleFactory.prototype.createVehicle = function (options) {
  
  if (options.vehicleType === "car") {
    this.vehicleClass = Car;
  } else {
    this.vehicleClass = Truck;
  }
  
  return new this.vehicleClass(options);
};