functionfoundry/fn/columnletter.js

Pure function JavaScript library

'use strict';

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = columnletter;

var _error = require('./error');

var _error2 = _interopRequireDefault(_error);

var _isnumber = require('./isnumber');

var _isnumber2 = _interopRequireDefault(_isnumber);

function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }

// Convert index to letter (e.g 0 -> A)
// Copyright 2015 JC Fisher

function columnletter(index) {

  if (!(0, _isnumber2.default)(index)) {
    return _error2.default.value;
  }

  // The column is determined by applying a modified Hexavigesimal algorithm.
  // Normally BA follows Z but spreadsheets count wrong and nobody cares.

  // Instead they do it in a way that makes sense to most people but
  // is mathmatically incorrect. So AA follows Z which in the base 10
  // system is like saying 01 follows 9.

  // In the least significant digit
  // A..Z is 0..25

  // For the second to nth significant digit
  // A..Z is 1..26

  var converted = "",
      secondPass = false,
      remainder,
      value = Math.abs(index);

  do {
    remainder = value % 26;

    if (secondPass) {
      remainder--;
    }

    converted = String.fromCharCode(remainder + 'A'.charCodeAt(0)) + converted;
    value = Math.floor((value - remainder) / 26);

    secondPass = true;
  } while (value > 0);

  return converted;
}
module.exports = exports['default'];