parse URL + absolutize URL in javascript (URLUtils shim - http://url.spec.whatwg.org/#url)

URLUtils.js

/*jslint regexp: true, maxerr: 50, indent: 2 */
 
(function (global) {
  "use strict";
  
  function URLUtils(url, baseURL) {
    var m = String(url).replace(/^\s+|\s+$/g, "").match(/^([^:\/?#]+:)?(?:\/\/(?:([^:@\/?#]*)(?::([^:@\/?#]*))?@)?(([^:\/?#]*)(?::(\d*))?))?([^?#]*)(\?[^#]*)?(#[\s\S]*)?/);
    if (!m) {
      throw new RangeError();
    }
    var protocol = m[1] || "";
    var username = m[2] || "";
    var password = m[3] || "";
    var host = m[4] || "";
    var hostname = m[5] || "";
    var port = m[6] || "";
    var pathname = m[7] || "";
    var search = m[8] || "";
    var hash = m[9] || "";
    if (baseURL !== undefined) {
      var base = new URLUtils(baseURL);
      var flag = protocol === "" && host === "" && username === "";
      if (flag && pathname === "" && search === "") {
        search = base.search;
      }
      if (flag && pathname.charAt(0) !== "/") {
        pathname = (pathname !== "" ? (((base.host !== "" || base.username !== "") && base.pathname === "" ? "/" : "") + base.pathname.slice(0, base.pathname.lastIndexOf("/") + 1) + pathname) : base.pathname);
      }
      // dot segments removal
      var output = [];
      pathname.replace(/^(\.\.?(\/|$))+/, "")
        .replace(/\/(\.(\/|$))+/g, "/")
        .replace(/\/\.\.$/, "/../")
        .replace(/\/?[^\/]*/g, function (p) {
          if (p === "/..") {
            output.pop();
          } else {
            output.push(p);
          }
        });
      pathname = output.join("").replace(/^\//, pathname.charAt(0) === "/" ? "/" : "");
      if (flag) {
        port = base.port;
        hostname = base.hostname;
        host = base.host;
        password = base.password;
        username = base.username;
      }
      if (protocol === "") {
        protocol = base.protocol;
      }
    }
    this.origin = protocol + (protocol !== "" || host !== "" ? "//" : "") + host;
    this.href = protocol + (protocol !== "" || host !== "" ? "//" : "") + (username !== "" ? username + (password !== "" ? ":" + password : "") + "@" : "") + host + pathname + search + hash;
    this.protocol = protocol;
    this.username = username;
    this.password = password;
    this.host = host;
    this.hostname = hostname;
    this.port = port;
    this.pathname = pathname;
    this.search = search;
    this.hash = hash;
  }
 
  global.URLUtils = URLUtils;
 
}(this));

Forked to fix a small bug: since pathname is guaranteed to start with /, adding an extra / before the leading part of base.pathname is unnecessary.

The following case breaks, as the @ gets detected as the auth part:

  https://service.domain.com/go?email=jim@jam.com

Suggested change is:

 var m = String(url).replace(/^\s+|\s+$/g, "").match(/^([^:\/?#]+:)?(?:\/\/(?:([^:@]*)(?::([^:@]*))?@)?(([^:\/?#]*)(?::(\d*))?))?([^?#]*)(\?[^#]*)?(#[\s\S]*)?/);

to

 var m = String(url).replace(/^\s+|\s+$/g, "").match(/^([^:\/?#]+:)?(?:\/\/(?:([^:@\/]*)(?::([^:@\/]*))?@)?(([^:\/?#]*)(?::(\d*))?))?([^?#]*)(\?[^#]*)?(#[\s\S]*)?/);

I'm not sure this is 100% correct though - better suggestions welcome.

@guybedford,
Thanks, good catch, I have updated my code.
the specification, written by Anne van Kesteren - https://url.spec.whatwg.org/#authority-state - tells, that "/", "", "?", and "#" should not be in "authority".

@Yaffle thanks so much for the quick response.

When updating to this new code in my tests, I've hit two more issues now unfortunately -

1. new URLUtils('asdf', 'http://example.org/test') gives an href of http://example.org//asdf instead of http://example.org/asdf
2. new URLUtils('asdf', 'file:///example.org/test') gives an href of file:/example.org/asdf instead of file:///example.org/asdf

These issues didn't happen in the original code that I'm still using though so will stick with that for now.

@guybedford, Thanks again,
I updated the code to fix those issues too. Possibly, there are other issues, I did not test well.
P.S. URLUtils tries to match URL API available in Chrome and Firefox - new URL('asdf', 'file:///example.org/test')

@Yaffle perhaps it is worth considering turning this into a polyfill repo?

@guybedford, there is one - https://github.com/Polymer/URL

A minor performance optimization for line 21 can be useful:

var base = baseURL instanceof URLUtils ? baseURL : new URLUtils(baseURL);