Factory Pattern

factory.js

// Types.js - Constructors used behind the scenes
 
// 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){
 
  this.state = options.state || "used";
  this.wheelSize = options.wheelSize || "large";
  this.color = options.color || "blue";
}
 
 
// FactoryExample.js
 
// Define a skeleton vehicle factory
function VehicleFactory() {}
 
// Define the prototypes and utilities for this factory
 
// Our default vehicleClass is Car
VehicleFactory.prototype.vehicleClass = Car;
 
// Our Factory method for creating new Vehicle instances
VehicleFactory.prototype.createVehicle = function ( options ) {
 
  switch(options.vehicleType){
    case "car":
      this.vehicleClass = Car;
      break;
    case "truck":
      this.vehicleClass = Truck;
      break;
    //defaults to VehicleFactory.prototype.vehicleClass (Car)
  }
 
  return new this.vehicleClass( options );
 
};
 
// Create an instance of our factory that makes cars
var carFactory = new VehicleFactory();
var car = carFactory.createVehicle( {
            vehicleType: "car",
            color: "yellow",
            doors: 6 } );
 
// Test to confirm our car was created using the vehicleClass/prototype Car
 
// Outputs: true
console.log( car instanceof Car );
 
// Outputs: Car object of color "yellow", doors: 6 in a "brand new" state
console.log( car );

factory.md

• creational pattern concerned with the notion of creating objects

when to use

• When our object or component setup involves a high level of complexity
• When we need to easily generate different instances of objects depending on the environment we are in
• When we're working with many small objects or components that share the same properties
• When composing objects with instances of other objects that need only satisfy an API contract (aka, duck typing) to work. This is useful for decoupling.