Force string to numeric-only string that can be converted to integer by replacing non-digits with integer character code

toDigits.js

function toDigits (str = '') {
  // replace every (/g) non-digit (\D) with the character code (charCodeAt) for that non-digit. 
  return str.replace(/\D/g, nondigit => nondigit.charCodeAt(0) );
}

console.log(toDigits('A1b2C3-4');