win-test.js

var gridOne = {
  cells: [
    ["x", "o", "o"],
    ["o", "x", "o"],
    ["x", "x", "o"],
  ],
  column: function(number) {
    number = number - 1;
    return [
      this.cells[0][number],
      this.cells[1][number],
      this.cells[2][number],
    ];
  },
  row: function(number) {
    number = number - 1;
    return this.cells[number];
  },
  diagonal: function(leftOrRight) {
    if (leftOrRight === "left") {
      return [
        this.cells[0][0],
        this.cells[1][1],
        this.cells[2][2],
      ];
    } else {
      return [
        this.cells[0][2],
        this.cells[1][1],
        this.cells[2][0],
      ];
    }
  },
};

console.log({winner: winCheck(gridOne)});

// a win is when all three consecutive cells have
// the same value, a 'run' is a collection of
// three cells in either a row or a column or a diagonal
function winCheck(board) {
  const result = runWin(board, 'column') || runWin(board, 'row');
  return result;
}

function runWin(board, run) {
  console.log('rows or columns');
  const allCells = [
    board[run](1), board[run](2), board[run](3),
  ];
  let winOrLoss = false;
  for (let index = 0; index < allCells.length; index++) {
    const theRun = allCells[index];
    const mark = theRun[0];
    winOrLoss = theRun.every(function(move) {
      return move === mark;
    });
    if (winOrLoss) { return winOrLoss; }
  }
  return winOrLoss;
}

function rowWin(board) {
  const allRows = [
    board.row(1), board.row(2), board.row(3),
  ];
  let winOrLoss = false;
  for (let index = 0; index < allRows.length; index++) {
    const theRow = allRows[index];
    const mark = theRow[0];
    winOrLoss = theRow.every(function(move) {
      return move === mark;
    });
    if (winOrLoss) { return winOrLoss; }
  }
  return winOrLoss;
}

function columnWin(board) {
  const allColumns = [
    board.column(1), board.column(2), board.column(3),
  ];
  let winOrLoss = false;
  for (let index = 0; index < allColumns.length; index++) {
    const theColumn = allColumns[index];
    const mark = theColumn[0];
    winOrLoss = theColumn.every(function(move) {
      return move === mark;
    });
    if (winOrLoss) { return winOrLoss; }
  }
  return winOrLoss;
}

function arrayCompare(first, second) {
  if (first.length !== second.length) { return false; }
  for (let index = 0; index < first.length; index++) {
    const firstValue = first[index];
    const secondValue = second[index];
    if (firstValue !== secondValue) { return false; }
  }
  return true;
}

function assertTrue(message, value) {
  if (typeof value === 'function') {
    value = value();
  }
  if (value) {
    console.log(`Success: ${message}`);
    return true;
  } else {
    console.log(`Failure: ${message}`);
    return false;
  }
}