Base58 encode/decode a decimal number

base58.js

var alphabet = "123456789abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ";
var base = alphabet.length; // base is the length of the alphabet (58 in this case)

// utility function to convert base 10 integer to base 58 string
function encode(num) {
  var encoded = '';
  while (num){
    var remainder = num % base;
    num = Math.floor(num / base);
    encoded = alphabet[remainder].toString() + encoded;
  }
  return encoded;
}

// utility function to convert a base 58 string to base 10 integer
function decode(str) {
  var decoded = 0;
  while (str){
    var index = alphabet.indexOf(str[0]);
    var power = str.length - 1;
    decoded += index * (Math.pow(base, power));
    str = str.substring(1);
  }
  return decoded;
}

module.exports.encode = encode;
module.exports.decode = decode;