Copyright 2016-2017, Caleb Evans
Released under the MIT License

This is the slickest Connect Four app around, written using HTML5, JavaScript, and Mithril. You can play on your phone or computer, with a friend or against the AI. Just be sure to enjoy and have fun. :)

You can play the app online at:
https://projects.calebevans.me/connect-four/

The entire app UI is constructed and managed in JavaScript using Mithril. Chip transitions are handled by CSS to maximize performance and smoothness. The grid layout is styled with CSS Flexbox to enable the stacking of grid elements from the bottom up.

Like many traditional board game AIs, my Connect Four AI uses the minimax algorithm. For my particular implementation, I've chosen to use a maximum search depth of three (meaning the AI examines possibilities up to three turns into the future). This is combined with alpha-beta pruning to dramatically reduce the number of possibilities evaluated.

My scoring heuristic works by counting connections of chips that intersect with an empty slot, giving exponentially more weight to larger connections. For example, every single chip touching an empty slot is worth four points, a connect-two is worth nine points, a connect-three is worth sixteen points, and so on. A winning connection of four or more chips is given the maximum/minimum score.

In the app, the AI player is lovingly referred to as "Mr. AI".

The project requires Node.js and Brunch, so make sure you have both.

brew install node

npm install -g brunch

From the cloned project directory, run:

npm install

To serve the app locally, run:

brunch watch --server

When run, the app will be accessible at http://localhost:3333.