excelColumnNameToInteger.js

// Converts Excel Column name to zero-based index
// A => 0, B => 1, Z => 25  AA => 26).

function excelColumnNameToInteger(columnName) {
  if !(/^[A-z]+$/.test(columnName)) {
    let result = 0;
    for (let i = 0; i < columnName.length; i++) {
      result += (columnName.charCodeAt(i) - 64) * Math.pow(26, columnName.length - i - 1);
    }
    return result - 1 // shift the result by 1 to get zero-based numbering;
  } else {
    throw new Error(`invalid columnName format: ${columnName}`)
  }
}