Obtém nome da coluna a partir do índice

main.js

function getColumnName (columnIndex) {
  let chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
	let base = chars.length;
  let output = "";

  while (0 <= columnIndex) {
    let remainder = columnIndex % base;
    columnIndex = Math.floor((columnIndex - remainder - 1) / base);

    output = chars[remainder] + output;
  }

  return output;
}