function URL(address, location, parser) {
  if (!(this instanceof URL)) {
    return new URL(address, location, parser);
  }

  var relative, extracted, parse, instruction, index, key
    , instructions = rules.slice()
    , type = typeof location
    , url = this
    , i = 0;

  //
  // The following if statements allows this module two have compatibility with
  // 2 different API:
  //
  // 1. Node.js's `url.parse` api which accepts a URL, boolean as arguments
  //    where the boolean indicates that the query string should also be parsed.
  //
  // 2. The `URL` interface of the browser which accepts a URL, object as
  //    arguments. The supplied object will be used as default values / fall-back
  //    for relative paths.
  //
  if ('object' !== type && 'string' !== type) {
    parser = location;
    location = null;
  }

  if (parser && 'function' !== typeof parser) parser = qs.parse;

  location = lolcation(location);

  //
  // Extract protocol information before running the instructions.
  //
  extracted = extractProtocol(address || '');
  relative = !extracted.protocol && !extracted.slashes;
  url.slashes = extracted.slashes || relative && location.slashes;
  url.protocol = extracted.protocol || location.protocol || '';
  address = extracted.rest;

  //
  // When the authority component is absent the URL starts with a path
  // component.
  //
  if (!extracted.slashes) instructions[2] = [/(.*)/, 'pathname'];

  for (; i < instructions.length; i++) {
    instruction = instructions[i];
    parse = instruction[0];
    key = instruction[1];

    if (parse !== parse) {
      url[key] = address;
    } else if ('string' === typeof parse) {
      if (~(index = address.indexOf(parse))) {
        if ('number' === typeof instruction[2]) {
          url[key] = address.slice(0, index);
          address = address.slice(index + instruction[2]);
        } else {
          url[key] = address.slice(index);
          address = address.slice(0, index);
        }
      }
    } else if (index = parse.exec(address)) {
      url[key] = index[1];
      address = address.slice(0, index.index);
    }

    url[key] = url[key] || (
      relative && instruction[3] ? location[key] || '' : ''
    );

    //
    // Hostname, host and protocol should be lowercased so they can be used to
    // create a proper `origin`.
    //
    if (instruction[4]) url[key] = url[key].toLowerCase();
  }

  //
  // Also parse the supplied query string in to an object. If we're supplied
  // with a custom parser as function use that instead of the default build-in
  // parser.
  //
  if (parser) url.query = parser(url.query);

  //
  // If the URL is relative, resolve the pathname against the base URL.
  //
  if (
      relative
    && location.slashes
    && url.pathname.charAt(0) !== '/'
    && (url.pathname !== '' || location.pathname !== '')
  ) {
    url.pathname = resolve(url.pathname, location.pathname);
  }

  //
  // We should not add port numbers if they are already the default port number
  // for a given protocol. As the host also contains the port number we're going
  // override it with the hostname which contains no port number.
  //
  if (!required(url.port, url.protocol)) {
    url.host = url.hostname;
    url.port = '';
  }

  //
  // Parse down the `auth` for the username and password.
  //
  url.username = url.password = '';
  if (url.auth) {
    instruction = url.auth.split(':');
    url.username = instruction[0] || '';
    url.password = instruction[1] || '';
  }

  url.origin = url.protocol && url.host && url.protocol !== 'file:'
    ? url.protocol +'//'+ url.host
    : 'null';

  //
  // The href is just the compiled result.
  //
  url.href = url.toString();
}
The actual URL instance. Instead of returning an object we've opted-in to
create an actual constructor as it's much more memory efficient and
faster and it pleases my OCD.

@constructor
@param {String} address URL we want to parse.
@param {Object|String} location Location defaults for relative paths.
@param {Boolean|Function} parser Parser for the query string.
@api public