In this lesson, we will integrate design patterns into a practical project: building a smart home system. You'll learn how to create and adapt various smart home devices using the Singleton, Builder, Composite, and Abstract Factory patterns in JavaScript. By the end, you will have a solid understanding of how these design patterns can make your smart home system more efficient, modular, and easier to maintain.

1. Singleton Pattern:

   • Purpose: Ensures a class has only one instance and provides a global point of access to it.
   • Steps:
     • Define a class (Singleton) with a static method to hold the single instance.
     • Implement the getInstance method to manage instance creation and access.

2. Builder Pattern:

   • Purpose: Constructs complex objects step by step, providing a flexible solution for object creation.
   • Steps:
     • Define a class (SmartHomeDevice) for the object.
     • Create a builder class (SmartHomeDeviceBuilder) with methods to set object properties and a method to return the final object.

3. Composite Pattern:

   • Purpose: Treats individual objects and compositions of objects uniformly.
   • Steps:
     • Define a base class (DeviceComponent) for the composite structure.
     • Implement LeafDevice for individual objects and CompositeDevice for composite objects.

4. Abstract Factory Pattern:

   • Purpose: Provides an interface for creating families of related or dependent objects without specifying their concrete classes.
   • Steps:
     • Define an abstract factory class (SmartDeviceFactory).
     • Implement concrete factories (LightFactory, FanFactory) to create specific sensor and actuator objects.

To start, we implement the Singleton pattern in JavaScript to ensure that a class has only one instance and provides a global point of access to it.

The getInstance method checks if an instance exists and creates one if it does not.

Next, we use the Builder pattern to construct complex SmartHomeDevice objects step by step.

The SmartHomeDeviceBuilder class provides methods to set device properties and construct the final SmartHomeDevice.

Now, we implement the Composite pattern to manage individual and composite objects uniformly.

The CompositeDevice class allows us to treat individual DeviceComponent objects uniformly as part of a composite structure.

Finally, we implement the Abstract Factory pattern to create families of related objects without specifying their concrete classes.

The LightFactory and FanFactory classes implement methods to create specific sensor and actuator objects.

Implementing Singleton, Builder, Composite, and Abstract Factory patterns in our smart home system allows us to create, organize, and manage devices in a structured and reusable manner. The Singleton pattern ensures a single instance of a class, the Builder pattern provides a flexible solution for object creation, the Composite pattern handles both individual and composite objects uniformly, and the Abstract Factory pattern creates families of related objects. This approach makes our smart home system more modular, flexible, and easier to maintain and extend.