npm install int-encoder

var en = require('int-encoder');

//simple integer conversion
en.encode(12345678); // "ZXP0"
en.decode('ZXP0'); // 12345678

//convert big hex number using optional base argument
en.encode('e6c6b53d3c8160b22dad35a0f705ec09', 16); // 'hbDcW9aE89tzLYjDgyzajJ'
en.decode('hbDcW9aE89tzLYjDgyzajJ', 16); // 'e6c6b53d3c8160b22dad35a0f705ec09'

public static class ShortCodes
{
    private static Random rand = new Random();

    // You may change the "shortcode_Keyspace" variable to contain as many or as few characters as you
    // please.  The more characters that aer included in the "shortcode_Keyspace" constant, the shorter
    // the codes you can produce for a given long.
const string shortcode_Keyspace = "abcdefghijklmnopqrstuvwxyz0123456789";

    // Arbitrary constant for the maximum length of ShortCodes generated by the application.
const int shortcode_maxLen = 12;


    public static string LongToShortCode(long number)
    {
        int ks_len = shortcode_Keyspace.Length;
        string sc_result = "";
        long num_to_encode = number;
        long i = 0;
        do
        {
            i++;
            sc_result = shortcode_Keyspace[(int)(num_to_encode % ks_len)] + sc_result;
            num_to_encode = ((num_to_encode - (num_to_encode % ks_len)) / ks_len);
        }
        while (num_to_encode != 0);
        return sc_result;
    }


    public static long ShortCodeToLong(string shortcode)
    {
        int ks_len = shortcode_Keyspace.Length;
        long sc_result = 0;
        int sc_length = shortcode.Length;
        string code_to_decode = shortcode;
        for (int i = 0; i < code_to_decode.Length; i++)
        {
            sc_length--;
            char code_char = code_to_decode[i];
            sc_result += shortcode_Keyspace.IndexOf(code_char) * (long)(Math.Pow((double)ks_len, (double)sc_length));
        }
        return sc_result;
    }
}