pattern-singleton.md

Singleton Pattern Tutorial: The Coffee Factory

Introduction

In this tutorial, we’ll learn about the Singleton design pattern using the example of a coffee factory. The Singleton pattern ensures that a class has only one instance and provides a global point of access to that instance. This is useful for managing shared resources, like a coffee factory, where only one instance should handle all coffee production.

Objective

You will implement a CoffeeFactory class as a singleton and write unit tests using Mocha with ts-mocha to verify its behavior.

Step-by-Step Guide

Step 1: Set Up the CoffeeFactory Class

1. Create a new file CoffeeFactory.ts and define the Singleton class.

   // CoffeeFactory.ts
   class CoffeeFactory {
     private static instance: CoffeeFactory;
   
     // Private constructor to prevent instantiation
     private constructor() {}
   
     // Method to get the singleton instance
     public static getInstance(): CoffeeFactory {
       if (!CoffeeFactory.instance) {
         CoffeeFactory.instance = new CoffeeFactory();
       }
       return CoffeeFactory.instance;
     }
   
     // Example method to simulate brewing coffee
     public brewCoffee(type: string): string {
       return `Brewing a cup of ${type}`;
     }
   }
   
   export default CoffeeFactory;