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Factory Pattern Overview
Factory Pattern Example
// 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 );
true
Car {doors: 6, state: "brand new", color: "yellow"}
var movingTruck = carFactory.createVehicle( {
vehicleType: "truck",
state: "like new",
color: "red",
wheelSize: "small" } );
// Test to confirm our truck was created with the vehicleClass/prototype Truck
// Outputs: true
console.log( movingTruck instanceof Truck );
// Outputs: Truck object of color "red", a "like new" state
// and a "small" wheelSize
console.log( movingTruck );
true
125 Truck {state: "like new", wheelSize: "small", color: "red"}
When To Use The Factory Pattern
- 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.
When Not To Use The Factory Pattern
Related JavaScript Design Patterns
- JavaScript Factory Pattern with Example //Popular
- JavaScript Builder Pattern Example //Popular
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