Factory Pattern (TS)

Definition

A pattern that provides an interface for creating objects in a superclass, but allows subclasses or logic gates to alter the type of objects that will be created.

Explain Like I'm New

A Factory is an automated vending machine. You don't need to know how the soda is made. You just press the 'Coke' button, and a Coke comes out. The Factory function abstracts away the messy `new` keywords and complex setup logic.

Real World Example

Building an API service factory. You call `ApiServiceFactory.create('user')` and it returns an Axios instance fully pre-configured with the User API base URL and specific Auth headers.

Common Use Cases

•Complex object initialization
•Decoupling implementation from usage

Interactive Example

// 1. The Common Interface
interface Notification {
  send(msg: string): void;
}

// 2. The Concrete Implementations
class EmailNotification implements Notification {
  send(msg: string) { console.log(`Sending Email: ${msg}`); }
}

class PushNotification implements Notification {
  send(msg: string) { console.log(`Sending Push: ${msg}`); }
}

// 3. The Factory
class NotificationFactory {
  // The return type is the broad Interface, hiding the specific classes
  public static create(type: "email" | "push"): Notification {
    if (type === "email") return new EmailNotification();
    if (type === "push") return new PushNotification();
    throw new Error("Unknown notification type");
  }
}

// Consumer code has no idea 'EmailNotification' class exists. 
// It just uses the factory.
const notifier = NotificationFactory.create("email");
notifier.send("Welcome to the app!");

Interview Questions

basic

Why use a Factory instead of just exporting multiple classes?

intermediate

How do you type the return value of a Factory?

advanced

What is an Abstract Factory in TypeScript?

Flash Cards

Question

How do you type the return value?

Click to reveal answer

Answer

You define a common `Interface` (e.g., `interface Button { render(): void }`). Both `MacButton` and `WindowsButton` implement that interface. The Factory's return type is explicitly typed as `Button`, hiding the specific class from the consumer.