case 'left': {
  (중략)
        if (prevData === cellData) { // 이전 숫자와 지금 숫자의 값이 같으면

          const score = parseInt($score.textContent);
          $score.textContent = score + currentRow.at(-1) * 2;

          currentRow[currentRow.length - 1] *= -2;
  (중략)
}
case 'right': {
  (중략)
        if (prevData === rowData[3 - j]) {

          const score = parseInt($score.textContent);
          $score.textContent = score + currentRow.at(-1) * 2;

          currentRow[currentRow.length - 1] *= -2;
  (중략)
}
case 'up': {
  (중략)
        if (prevData === cellData) {

          const score = parseInt($score.textContent);
          $score.textContent = score + currentRow.at(-1) * 2; 

          currentRow[currentRow.length - 1] *= -2;