Record row updated time automatically

RowUpdated.gs

// 업데이트 날짜를 적을 Column
var UPDATED_COLUMN = 'B';
// 실제 데이터가 있다고 판단할 Column
// 여기가 비어있으면 업데이트 날짜를 적지 않는다.
var DATA_COLUMN = 'C';
// 시트의 헤더 영역 Row 수 
var HEADER_ROW_LENGTH = 7; 

function onEdit(e) {
  var sheet = SpreadsheetApp.getActiveSheet();
  var cell = sheet.getActiveCell();
  var updatedCell = sheet.getRange(cell.getRowIndex(), columnLetter2Number(UPDATED_COLUMN));
  var dataCell = sheet.getRange(cell.getRowIndex(), columnLetter2Number(DATA_COLUMN));
  if (cell.getRowIndex() >= HEADER_ROW_LENGTH && dataCell.getValue().length > 0) {
    updatedCell.setValue(new Date()).setNumberFormat("yyyy/MM/DD HH:mm")
  }
}

// 1 -> A
function columnNumber2Letter(column) {
  var temp, letter = '';
  while (column > 0)
  {
    temp = (column - 1) % 26;
    letter = String.fromCharCode(temp + 65) + letter;
    column = (column - temp - 1) / 26;
  }
  return letter;
}

// A -> 1
function columnLetter2Number(letter) {
  var base = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', i, j, result = 0;
  for (i = 0, j = letter.length - 1; i < letter.length; i += 1, j -= 1) {
    result += Math.pow(base.length, j) * (base.indexOf(letter[i]) + 1);
  }
  return result;
}