Factory Method
Factory Method separates object creation from the workflow that uses the object, allowing a subtype or configuration to choose the concrete product.
10 patterns · Creational / Structural / Behavioral
Design patterns, explained as logic.
Every pattern from Head First Design Patterns rebuilt as PROBLEM → RULE → RUN → OUTPUT, with an original TypeScript example, honest trade-offs, and the exact condition where the abstraction stops paying rent.
Creational
Creational patterns
Structural
Structural patterns
Decorator
Decorator wraps an object with optional layers, allowing capabilities to be combined at runtime without creating a subclass for every combination.
Adapter
Adapter converts an existing interface into the interface a client expects, containing incompatibility at one explicit system boundary.
Facade
Facade offers a small task-oriented interface over a complicated subsystem, reducing the knowledge each caller needs for common workflows.
Behavioral
Behavioral patterns
Strategy
When one task has several valid ways to run, Strategy keeps the workflow stable while the decision-making rule can change independently.
Observer
Observer turns a state change into a broadcast so multiple dependents can react without the source knowing their concrete implementations.
Command
Command packages a request as an object so actions can be queued, logged, retried, composed, or reversed independently from the caller.
Template Method
Template Method defines a stable algorithm sequence while allowing selected steps to vary through subclass hooks or overrides.
Iterator
Iterator provides a standard way to traverse a collection while hiding whether the underlying structure is an array, tree, stream, or remote page.