CODE EXAMPLE FOR JAVASCRIPT

javascript alphabet to number

/**
 * Converts a spreadsheet column letter to a number. eg. A -> 1
 * 
 * @param {String} str - (required) The spreadsheet column letter to convert to a number.
 * 
 * @returns {(Number|undefined)} The column number or undefined.
 */
function convertLetterToNumber(str) {
  if ((typeof str === "string" || str instanceof String) && /^[a-zA-Z]+$/.test(str)) {
    str = str.toUpperCase();
    let out = 0,
      len = str.length;
    for (pos = 0; pos < len; pos++) {
      out += (str.charCodeAt(pos) - 64) * Math.pow(26, len - pos - 1);
    }
    return out;
  } else {
    return undefined;
  }
}

convertLetterToNumber("A"); // 1
convertLetterToNumber("b"); // 2
convertLetterToNumber("Ba"); // 53
convertLetterToNumber("dE"); // 109
convertLetterToNumber("ZZZZ"); // 475254

convertLetterToNumber("A"); // 1
convertLetterToNumber("b"); // 2
convertLetterToNumber("Ba"); // 53
convertLetterToNumber("dE"); // 109
convertLetterToNumber("ZZZZ"); // 475254