Design Patterns Every Developer Should Know

The Three Families of GoF Patterns

Design patterns are proven recipes for recurring software design problems. This guide groups the classic GoF patterns into three families.

Creational Patterns

Control object creation: Singleton, Factory Method, Abstract Factory, Builder, Prototype.

// Builder pattern in TypeScript
class QueryBuilder {
  private query = { select: "*", where: "", limit: 10 };
  where(condition: string) { this.query.where = condition; return this; }
  limit(n: number) { this.query.limit = n; return this; }
  build() { return this.query; }
}

Structural Patterns

Compose objects and classes: Adapter, Decorator, Proxy, Facade, Bridge, Composite, Flyweight.

Behavioural Patterns

Define communication between objects: Observer, Strategy, Command, Chain of Responsibility, Iterator, State, Template Method, Visitor, Mediator, Memento, Interpreter.

Each pattern is illustrated with a minimal TypeScript snippet and a clear "when to use" note, making this the ideal desk reference for code reviews and system design interviews.