Simple shortener of an integer string into a base62 string. Sample usage at bottom of each file.

url_shortener.js

var codeset  = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
var base = codeset.length;

function encode(intStr) {
  var hash = "";
  intStr = parseInt(intStr);
  while (intStr > 0) {
    hash = self.codeset[parseInt(intStr % base)] + hash;
    intStr = Math.floor(intStr / base);
  }
  return hash;
}

function decode(encoded) {
  var intStr = 0;

  for (var i = 0; i < encoded.length; i++) {
    var char, n, power;

    char = encoded[i];

    n = codeset.indexOf(char);

    if (n == -1) {
      return -1; // bad hash
    }

    power = (encoded.length-1)-i;
    intStr += n * Math.pow(base, power);
  }
  return parseInt(intStr);
}

var result = encode("12345");
console.log("encode '12345' = "+result);
console.log("decode "+result+" = "+decode(result));

url_shortener.rb

@codeset  = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
@base = @codeset.length

def encode(intStr)
  hash = ""
  while (intStr.to_i > 0)
    hash = "#{@codeset[(intStr % @base).to_i]}#{hash}"
    intStr = (intStr.to_i / @base).floor
  end

  return hash;
end

def decode(encoded)
  intStr = 0
  encoded = encoded.split('')
  (0..encoded.length-1).each do |i|
    char = encoded[i]
    n = @codeset.index(char)

    return nil if n.nil?  # bad hash
    
    power = (encoded.length-1)-i
    intStr += n * (@base ** power)
  end

  return intStr.to_i
end



result = encode("12345")
puts("'12345' encodes to: #{result}")
puts("#{result} decodes to: #{decode(result)}")