code: function convertR1C1toA1 (ref) {
    if (!R1C1.test(ref)) {
      throw new Error(`${ref} is not a valid R1C1 cell reference`)
    }
  
    var refParts = ref
      .replace(R1C1, '$1,$2')
      .split(',')
  
    var row = refParts[0]
    var column = refParts[1]
    var columnStr = ''
  
    for (; column; column = Math.floor((column - 1) / 26)) {
      columnStr = String.fromCharCode(((column - 1) % 26) + 65) + columnStr
    }
  
    return columnStr + row
  }
docs: Convert R1C1 notation to A1 notation
  
  @param {String} ref
  @returns {String}
  @throws {Error}