md5.js

var MD5 = function() {
  var crypto = require('crypto');
  return {
    hex: function(src) {
      var md5 = crypto.createHash('md5');
      md5.update(src, 'utf8');
      return md5.digest('hex');
    }
  };
};

if (require.main === module) {
  console.log(MD5().hex(process.argv[2]));
} else {
  module.exports = MD5;
}

from console

node md5.js "hoge"

from program

var MD5 = require('md5.js');
MD5().hex('hoge');