columnletter.js

columnletter.js

import { ERRORTYPES as error } from "./error";
import isnumber from "./isnumber";

Convert index to letter (e.g 0 -> A)

export default function columnletter(index) {
  if (!isnumber(index)) {
    return error.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;
}