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README

The primary purpose of this repo is to practice using JavaScript factory functions and modules. Project guidelines found here: https://www.theodinproject.com/lessons/javascript-tic-tac-toe

Features

  • Game modes
    • Play against AI that makes a random move (easy mode, default).
    • Play against AI that uses minimax algorithm to choose the best move (hard mode, unbeatable).
    • Alternate turns with a human player.
  • Keeps track of each player's score
  • Highlights winning line

Code

Code is organized using IIFE modules (Gameboard, DisplayController) and JavaScript factory functions (player, computerPlayer, game).

I decided to keep important information within the game factory's state object.

Getting minimax function to align with an optimal move

My implementation of minimax

This was the most challenging aspect of this project. I found that I could easily enough replace the pseudocode for the algorithm found on Wikipedia with JavaScript, and I could get it to return a heuristic value of 1, -1, or 0. However, associating that value with the optimal move proved challenging.

At first I thought I needed to generate the entire game tree prior to calling minimax, then I realized that minimax will do this for me if I generate next board states with legal moves within minimax.

I was able to associate the return value with an optimal move when I realized that I could store moves and scores in two separate arrays: Each move's index would line up with its associated score in the scores array. Then, minimaxChoice = moves[maxScoreIndex]; for the maximizing player, and minimaxChoice = moves[minScoreIndex]; for the minimizing player.