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JavaScript Factory Pattern

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The Factory Pattern suggests defining an interface for creating an object where you allow the subclasses to decide which class to instantiate. This pattern handles the problem by defining a completely separate method for the creation of objects and which sub-classes are able to override so they can specify the ‘type’ of factory product that will be created.

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  1. function VehicleFactory() {}
  2.  
  3. VehicleFactory.prototype.vehicleClass = Car;
  4. VehicleFactory.prototype.getVehicle = function (options) {
  5.     return new this.vehicleClass(options);
  6. };
  7.  
  8. var carFactory = new VehicleFactory();
  9. var car = carFactory.getVehicle({ color: "yellow", turbo: true });
  10.  
  11. console.log(car instanceof Car); // => true
  12.  
  13. // approach #1: Modify a VehicleFactory instance to use the Truck class
  14. carFactory.vehicleClass = Truck;
  15. var mover = carFactory.getVehicle({ enclosedCargo: true, length: 26 });
  16. counsole.log(mover instanceof Truck); // => true
  17.  
  18. // approach #2: Subclass VehicleFactory to create a factory class that
  19. // builds Trucks
  20. function TruckFactory () {}
  21.  
  22. TruckFactory.prototype = new VehicleFactory();
  23. TruckFactory.prototype.vehicleClass = Truck;
  24.  
  25. var truckFactory = new TruckFactory();
  26. var bigfoot = truckFactory.getVehicle({ monster: true, cylinders: 12 });
  27.  
  28. console.log(bigfoot instanceof Truck); // => true

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