OOP Patterns: A Board Game Demo

This demo is inspired by Kevin Berridge’s talk OOP: You’re Doing It Completely Wrong. If you haven’t watched it, it’s worth an hour of your time.

The idea: model a board game using proper object-oriented design. Objects that know their own responsibilities. No god objects. No procedural code dressed up in classes.

The pieces

Player — knows how to play a game. Rolls dice, reads the result, announces what happened. Doesn’t know what game it’s playing or how dice work internally.

Die / DieFactory — a die knows how to roll itself. The factory builds dice with a given number of sides. The random number generator is injected, so tests can use a fake that always returns max or min.

Game — manages turn order. Tells each player when it’s their turn and hands them the dice.

Monopoly — a specific game. Has a name, owns two six-sided dice. Could be Yahtzee or anything else with the same interface.

UserInterface / UserView — decoupled output. The same say() call goes to both the browser’s <ul> and the console. Swap out either without touching game logic.

What makes it interesting

The RandomNumberGenerator is injected into Die. That single seam makes the whole thing testable without mocking globals. FakeMath_RandomReturnsMax and FakeMath_RandomReturnsMin are two-line objects that let you assert exact outcomes in tests.

The Flag object is a small thing worth noticing — a boolean with named methods (isTrue(), isFalse(), toggle()). Reads like intent, not implementation. Better than if (readyToExecute === true) scattered everywhere.

Try it

// The entry point — wires everything together
var fred = new Player("Fred", userInterface);
var barney = new Player("Barney", userInterface);

fred.playGame(game);
barney.playGame(game);

Fred and Barney each take a turn. They roll two dice, read the total, announce the result. The game logs every step to the console and appends it to the page.

The patterns here — constructor injection, interface-based design, single responsibility — are the same ones I use in C# every day. JavaScript just makes the seams more visible because there’s no compiler enforcing the contracts.