Cannot get minimax function to work for tic tac toe game

const grabEmptySquares = (array) => {    var emptyGameSquares = [];    for (i = 0; i < 9; i++) {      if (!array[i]) emptyGameSquares.push(i);    }    return emptyGameSquares;  };    function findBestMove(board) {    var bestMove = {      index: null,      evaluation: null,    };    var availableMoves = grabEmptySquares(board);    availableMoves.forEach((move) => {      const simulGameboard = JSON.parse(JSON.stringify(board));      simulGameboard[move] = "o";      const evaluation = minimax(simulGameboard, 1, false);      const moveDetails = {        index: move,        evaluation: evaluation,      };      console.log(moveDetails)        if (evaluation > bestMove.evaluation || bestMove.evaluation === null) {        bestMove.index = move;        bestMove.evaluation = evaluation;      }    });      return bestMove.index;  }    function evaluate(board, isMaximizingPlayer, depth) {    var gameStatus = isGameOver(board);    if (gameStatus[0] != true) return;    if (gameStatus[1] === "win")      return isMaximizingPlayer ? +10 - depth : -10 + depth;    if (gameStatus[1] === "tie") return 0;  }    function minimax(board, depth, isMaximizingPlayer) {    var gameStatus = isGameOver(board);    if (gameStatus[0] == true) {      const evaluation = evaluate(board, !isMaximizingPlayer, depth);      return evaluation;    }      var simulGameboard = JSON.parse(JSON.stringify(board));    var availableMoves = grabEmptySquares(simulGameboard);      if (isMaximizingPlayer) {      bestVal = -Infinity;      availableMoves.forEach((move) => {        depth % 2 === 0          ? (simulGameboard[move] = "o")          : (simulGameboard[move] = "x");        value = minimax(simulGameboard, depth + 1, false);        bestVal = Math.max(bestVal, value);          const moveDetails = {          index: move,          evaluation: bestVal,          depth: depth,        };        console.log(moveDetails);      });      return bestVal;    } else {      bestVal = Infinity;      availableMoves.forEach((move) => {        depth % 2 === 0          ? (simulGameboard[move] = "o")          : (simulGameboard[move] = "x");          value = minimax(simulGameboard, depth + 1, true);        bestVal = Math.min(bestVal, value);          const moveDetails = {          index: move,          evaluation: bestVal,          depth: depth,        };        console.log(moveDetails);      });      return bestVal;    }  }    function isGameOver(array) {    var gameOver = false;    if (      (array[0] && array[0] === array[1] && array[0] === array[2]) ||      (array[3] && array[3] === array[4] && array[3] === array[5]) ||      (array[6] && array[6] === array[7] && array[6] === array[8])    ) {      return (gameOver = [true, "win"]);    }    if (      (array[0] && array[0] === array[4] && array[0] === array[8]) ||      (array[2] && array[2] === array[4] && array[2] === array[6])    ) {      return (gameOver = [true, "win"]);    }    if (      (array[1] && array[1] === array[4] && array[4] === array[7]) ||      (array[0] && array[0] === array[3] && array[3] === array[6]) ||      (array[2] && array[2] === array[5] && array[5] === array[8])    ) {      return (gameOver = [true, "win"]);    }    if ([...array].every((index) => index)) {      return (gameOver = [true, "tie"]);    }    return (gameOver = [false, null]);  }  

I followed https://www.geeksforgeeks.org/minimax-algorithm-in-game-theory-set-3-tic-tac-toe-ai-finding-optimal-move/ for direction, and as far as I can see, the logic is the same.

Still, my code doesn't come up with the correct moves. The evaluation my minimiax function gives to each move is wrong. And it is sooo wrong I cannot even begin to figure out where the code is off. Please help. I've spent the last two weeks working on this.

Ex:

var gameboard = [ null, "o", null, "x", "x", null, null, null, null ]    If I run findBestMove(gameboard), the expected output should be    bestMove = {index: 5,              evaluation: 0}    What I get instead is     bestMove = {index: 1,              evaluation: -8}.    In fact, every single move has the same evaluation.   

https://stackoverflow.com/questions/66977730/cannot-get-minimax-function-to-work-for-tic-tac-toe-game April 07, 2021 at 07:26AM