to calculate excel column name from numbers

numToColumn.js

/**
 * Takes a positive integer and returns the corresponding column name.
 * @param {number} num  The positive integer to convert to a column name.
 * @return {string}  The column name.
 */
function toColumnName(num) {
  for (var ret = '', a = 1, b = 26; (num -= a) >= 0; a = b, b *= 26) {
    ret = String.fromCharCode(parseInt((num % b) / a) + 65) + ret;
  }
  return ret;
}

//  toColumnName(1) 'A'
//  toColumnName(26) 'Z'
//  toColumnName(27) 'AA'