get_a1

function columnToLetter(column){
  var temp, letter = '';
  while (column > 0){
    temp = (column - 1) % 26;
    letter = String.fromCharCode(temp + 65) + letter;
    column = (column - temp - 1) / 26;
  }
  return letter;
}
function to_a1(row, col, rowcount, colcount){
  if(typeof(row)== "number" && typeof(col)== "number" && row >0 && col>0 ){
    var ocol = col;
    if(col !== null){col = columnToLetter(col);}
    var a1 = col+row;
    if(colcount !== null){
      colcount = columnToLetter(ocol+colcount-1);
      if(rowcount !== null){a1+=":"+colcount+(row+rowcount-1);}else{a1+=":"+colcount+row;}
    }
    Logger.log(a1);
    return a1;
  }else{
    throw 'to_a1 requires row and col to be positive numbers';
  }
}