js convert number to alphabet code example

Example 1: javascript alphabet to number

function convertLetterToNumber(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;
}

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

Example 2: js int to alphabet

var value = 10;

document.write((value + 9).toString(36).toUpperCase());