Factory Pattern

class-factory.js

/**
 * The factory pattern abstracts object creation by providing an interface, where we can specify the type of 
 * factory object to be created.
 *
 * The Factory pattern can be especially useful when applied to the following situations:
 *
 * - When our object or component setup involves a high level of complexity, 
 *   e.g. if it strongly depends on dynamic factors or application configuration.
 * - 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.
 */

class Car {
 constructor(doors, state, color) {
     this.doors = doors || 4;
     this.state = state || "brand new";
     this.color = color || "silver";
 }

 props(){
    return `I am a ${this.state} ${this.color} car and I have ${this.doors} doors`
 }
}
    
// A class for defining new trucks
class Truck {
 constructor(state, wheelSize, color) {
     this.state = state || "used";
     this.wheelSize = wheelSize || "large";
     this.color = color || "blue";
 }

 props(){
    return `I am a ${this.state} ${this.color} truck and I have a ${this.wheelSize} wheels`
 }
}
    
// Define a factory

class VehicleFactory {
 constructor(options) {
     let vehicle;
     switch (options.type) {
         case "car":
            vehicle = new Car(options.doors, options.state, options.color)
            break;
         case "truck":
            vehicle = new Truck(options.state, options.wheelSize, options.color);
            break;
        }
     return vehicle;
     }
}
    
// Usage

let options1 = {
 type: "car",
 color: "yellow",
 doors: 6
}
let options2 = {
 type: "truck",
 state: "like new",
 color: "red",
 wheelSize: "small"
}
    
let car = new VehicleFactory(options1);
let truck = new VehicleFactory(options2);

console.log(car.state) // brand new
console.log(car.color) // yellow
console.log(car.props()) // I am a brand new yellow car and I have 6 doors
console.log(truck.state) // used
console.log(truck.color)// red
console.log(truck.props())// I am a used red truck and I have a small wheels