Last Updated: February 25, 2016
· timsommer

JavaScript factory pattern

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.

jsfiddle link:

function VehicleFactory() {}
VehicleFactory.prototype.vehicleClass = Car;
VehicleFactory.prototype.getVehicle = function (options) {
    return new this.vehicleClass(options);

var carFactory = new VehicleFactory();
var car = carFactory.getVehicle({
    color: "yellow",
    turbo: true

console.log(car instanceof Car); // => true

// approach #1: Modify a VehicleFactory instance to use the Truck class
carFactory.vehicleClass = Truck;
var mover = carFactory.getVehicle({
    enclosedCargo: true,
    length: 26
counsole.log(mover instanceof Truck); // => true

// approach #2: Subclass VehicleFactory to create a factory class that
// builds Trucks
function TruckFactory() {}

TruckFactory.prototype = new VehicleFactory();
TruckFactory.prototype.vehicleClass = Truck;

var truckFactory = new TruckFactory();
var bigfoot = truckFactory.getVehicle({
    monster: true,
    cylinders: 12

console.log(bigfoot instanceof Truck); // => true