Blog

Why inheritance hierarchies explode when behaviours combine, how composing small objects avoids it, and when inheritance is still the right tool. With the arithmetic, the fragile base class problem, and decorators in TypeScript.

How a subject notifies a list of observers through a small interface, so new reactions can be added without editing the code that triggers them. Implementing it in TypeScript, its pitfalls — ordering, errors, leaks, re-entrancy — and how it relates to event emitters, pub/sub and the DOM.

Five principles for object-oriented design, applied one at a time to a single order service. What each one actually prevents, how to spot a violation in a code review, and when following them blindly makes code worse.

A vending machine, an order, a TCP connection: objects that respond to the same event differently depending on what happened before. How to model them as explicit state machines, implement them with the State pattern or a transition table, and stop invalid states from existing.

When one step of an algorithm varies — pricing, sorting, retry policy, compression — the Strategy pattern puts each variant behind an interface and picks one at runtime. How it works, how it looks in TypeScript with classes or plain functions, and when a switch statement is still better.