在对/错语句上返回正确的值

Question

I am meant to be getting "Player X Won!" but it keeps returning "Player O Won!", even though I switch turns after each player move. My tests keep failing as a result. I've tried to switch turns just before showWinner() and also in checkWinner() but nothing seems to change the result

function Game() {
  this.current_player = "X";
  this.grid = [[null, null, null], [null, null, null], [null, null, null]];
  this.move_counter = 0;
}

Game.prototype.currentPlayer = function() {
  return this.current_player;
};

Game.prototype.switchTurn = function() {
  if (this.currentPlayer() === "X") {
    this.current_player = "O";
  } else if (this.currentPlayer() === "O") {
    this.current_player = "X";
  }
};

Game.prototype.showGrid = function() {
  return this.grid;
};

Game.prototype.playerMove = function(row, column) {
  this.grid[row][column] = this.currentPlayer();
  this.move_counter++;
  this.switchTurn();
  this.showWinner();
};

Game.prototype.moveCounter = function() {
  return this.move_counter;
};

Game.prototype.checkWinner = function() {
  for(var i = 0; i < this.grid.length; i++) {
    if (this.grid[i][0] != null && this.grid[i][0] === (this.grid[i][1] && this.grid[i][2])) {
      return true
    } else if (this.grid[0][i] != null && this.grid[0][i] === (this.grid[1][i] && this.grid[2][i])) {
      return true
    } else if (this.grid[0][0] != null && this.grid[0][0] === (this.grid[1][1] && this.grid[2][2])) {
      return true
    } else if (this.grid[2][0] != null && this.grid[2][0] === (this.grid[1][1] && this.grid[0][2])) {
      return true
    } else {
      return false
    }
  }
};

Game.prototype.showWinner = function() {
  if (this.checkWinner() === true) {
    this.switchTurn();
    return "Player " + this.current_player + " Won!";
  }
};

Game.prototype.checkDraw = function() {
  if (this.moveCounter() === 9) {
    return "It's a draw!"
  } else {
    return null
  }
};

Answer 1

Maybe remove this.switchTurn(); line in showWinner function ?

I would also put showWinner() call before switchTurn() in playerMove

EDIT: I just noticed, your conditions in checkWinner are all wrong. You are comparing a string with a boolean. You need to compare the grid content with this.currentPlayer() .