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Last Updated: November 21, 2025

Design Patterns

Software design patterns

Creational Patterns

Item	Description
`Singleton`	Single instance of a class
`Factory`	Create objects without specifying class
`Abstract Factory`	Families of related objects
`Builder`	Construct complex objects step-by-step
`Prototype`	Clone existing objects

Structural Patterns

Item	Description
`Adapter`	Interface between incompatible classes
`Bridge`	Separate abstraction from implementation
`Composite`	Tree structure of objects
`Decorator`	Add behavior dynamically
`Facade`	Simplified interface to complex system
`Proxy`	Placeholder for another object

Behavioral Patterns

Item	Description
`Observer`	Subscribe to events
`Strategy`	Interchangeable algorithms
`Command`	Encapsulate requests as objects
`State`	Change behavior based on state
`Chain of Responsibility`	Pass request along chain
`Iterator`	Access elements sequentially
`Mediator`	Centralized communication

Singleton Example

class Singleton {
    private static instance: Singleton;
    
    private constructor() {}
    
    static getInstance(): Singleton {
        if (!Singleton.instance) {
            Singleton.instance = new Singleton();
        }
        return Singleton.instance;
    }
}

// Factory Example
interface Product {
    operation(): string;
}

class ConcreteProductA implements Product {
    operation(): string {
        return 'Product A';
    }
}

class Factory {
    createProduct(type: string): Product {
        if (type === 'A') return new ConcreteProductA();
        throw new Error('Invalid type');
    }
}

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