Numerous design patterns let you extend functionality; for example, in Java Design Patterns you’ve seen how to extend functionality with the Proxy, Decorator, and Strategy patterns.

Implementing Strategy Pattern and Callbacks in TypeScript. The TypeScript datatyping support not only applies to simple variables, it also supports you when doing clever things with functions.

Once you start working with the "classic" design patterns (the ones listed in the book "Design Patterns: Elements of Reusable Object-Oriented Software" by Gamma, Helm, Johnson and Vlissides ...