Convert alphabetical spreadsheet column ID to a numeric index (Google Sheets, etc)

spreadsheetIndexfromColumn.js

// given a column 'A'...'AB' etc, return a numeric index
function columnToIndex(column) {
  // Initialize the index to 0
  var index = 0;

  // Iterate through the characters in the column string
  for (var i = 0; i < column.length; i++) {
    // Get the character at the current index
    var char = column.charAt(i);

    // Convert the character to a number (A = 1, B = 2, etc.)
    var num = char.charCodeAt(0) - 64;

    // Multiply the number by 26 to the power of the index
    // (A = 1, AA = 26, AAA = 676, etc.)
    num *= Math.pow(26, column.length - i - 1);

    // Add the number to the index
    index += num;
  }

  // Return the index
  return index-1;
}