Decorator Design Pattern Explained

Decorator lets you attach new behavior to an object dynamically by wrapping it in another object with the same interface, without modifying the original class.

Why it exists

• Subclassing to add every possible combination of optional behavior leads to an explosion of subclasses

How to apply it

• Wrap the base object in one or more decorator objects, each adding a bit of behavior while still exposing the original interface
• Multiple decorators can be layered, combining their effects in the order they're applied

FAQ

Is middleware an example of the Decorator pattern?

Conceptually yes — each middleware wraps the next one, adding behavior around it while preserving a common request/response interface.