Polyfill for JavaScript URL. The URL interface is used to parse, construct, normalize, and encode URLs.

/* Any copyright is dedicated to the Public Domain.
 * http://creativecommons.org/publicdomain/zero/1.0/ */

 /** @type {boolean|undefined} */
Window.prototype.forceJURL = false;

(function(scope) {
  'use strict';

  // feature detect for URL constructor
  var hasWorkingUrl = false;
  if (!scope.forceJURL) {
    try {
      var u = new URL('b', 'http://a');
      u.pathname = 'c%20d';
      hasWorkingUrl = u.href === 'http://a/c%20d';
    } catch(e) {}
  }

  if (hasWorkingUrl)
    return;

  var relative = Object.create(null);
  relative['ftp'] = 21;
  relative['file'] = 0;
  relative['gopher'] = 70;
  relative['http'] = 80;
  relative['https'] = 443;
  relative['ws'] = 80;
  relative['wss'] = 443;

  var relativePathDotMapping = Object.create(null);
  relativePathDotMapping['%2e'] = '.';
  relativePathDotMapping['.%2e'] = '..';
  relativePathDotMapping['%2e.'] = '..';
  relativePathDotMapping['%2e%2e'] = '..';

  function isRelativeScheme(scheme) {
    return relative[scheme] !== undefined;
  }

  function invalid() {
    clear.call(this);
    this._isInvalid = true;
  }

  function IDNAToASCII(h) {
    if ('' == h) {
      invalid.call(this)
    }
    // XXX
    return h.toLowerCase()
  }

  function percentEscape(c) {
    var unicode = c.charCodeAt(0);
    if (unicode > 0x20 &&
       unicode < 0x7F &&
       // " # < > ? `
       [0x22, 0x23, 0x3C, 0x3E, 0x3F, 0x60].indexOf(unicode) == -1
      ) {
      return c;
    }
    return encodeURIComponent(c);
  }

  function percentEscapeQuery(c) {
    // XXX This actually needs to encode c using encoding and then
    // convert the bytes one-by-one.

    var unicode = c.charCodeAt(0);
    if (unicode > 0x20 &&
       unicode < 0x7F &&
       // " # < > ` (do not escape '?')
       [0x22, 0x23, 0x3C, 0x3E, 0x60].indexOf(unicode) == -1
      ) {
      return c;
    }
    return encodeURIComponent(c);
  }

  var EOF = undefined,
      ALPHA = /[a-zA-Z]/,
      ALPHANUMERIC = /[a-zA-Z0-9\+\-\.]/;

  /**
   * @param {!string} input
   * @param {?string=} stateOverride
   * @param {(URL|string)=} base
   */
  function parse(input, stateOverride, base) {
    function err(message) {
      errors.push(message)
    }

    var state = stateOverride || 'scheme start',
        cursor = 0,
        buffer = '',
        seenAt = false,
        seenBracket = false,
        errors = [];

    loop: while ((input[cursor - 1] != EOF || cursor == 0) && !this._isInvalid) {
      var c = input[cursor];
      switch (state) {
        case 'scheme start':
          if (c && ALPHA.test(c)) {
            buffer += c.toLowerCase(); // ASCII-safe
            state = 'scheme';
          } else if (!stateOverride) {
            buffer = '';
            state = 'no scheme';
            continue;
          } else {
            err('Invalid scheme.');
            break loop;
          }
          break;

        case 'scheme':
          if (c && ALPHANUMERIC.test(c)) {
            buffer += c.toLowerCase(); // ASCII-safe
          } else if (':' == c) {
            this._scheme = buffer;
            buffer = '';
            if (stateOverride) {
              break loop;
            }
            if (isRelativeScheme(this._scheme)) {
              this._isRelative = true;
            }
            if ('file' == this._scheme) {
              state = 'relative';
            } else if (this._isRelative && base && base._scheme == this._scheme) {
              state = 'relative or authority';
            } else if (this._isRelative) {
              state = 'authority first slash';
            } else {
              state = 'scheme data';
            }
          } else if (!stateOverride) {
            buffer = '';
            cursor = 0;
            state = 'no scheme';
            continue;
          } else if (EOF == c) {
            break loop;
          } else {
            err('Code point not allowed in scheme: ' + c)
            break loop;
          }
          break;

        case 'scheme data':
          if ('?' == c) {
            this._query = '?';
            state = 'query';
          } else if ('#' == c) {
            this._fragment = '#';
            state = 'fragment';
          } else {
            // XXX error handling
            if (EOF != c && '\t' != c && '\n' != c && '\r' != c) {
              this._schemeData += percentEscape(c);
            }
          }
          break;

        case 'no scheme':
          if (!base || !(isRelativeScheme(base._scheme))) {
            err('Missing scheme.');
            invalid.call(this);
          } else {
            state = 'relative';
            continue;
          }
          break;

        case 'relative or authority':
          if ('/' == c && '/' == input[cursor+1]) {
            state = 'authority ignore slashes';
          } else {
            err('Expected /, got: ' + c);
            state = 'relative';
            continue
          }
          break;

        case 'relative':
          this._isRelative = true;
          if ('file' != this._scheme)
            this._scheme = base._scheme;
          if (EOF == c) {
            this._host = base._host;
            this._port = base._port;
            this._path = base._path.slice();
            this._query = base._query;
            this._username = base._username;
            this._password = base._password;
            break loop;
          } else if ('/' == c || '\\' == c) {
            if ('\\' == c)
              err('\\ is an invalid code point.');
            state = 'relative slash';
          } else if ('?' == c) {
            this._host = base._host;
            this._port = base._port;
            this._path = base._path.slice();
            this._query = '?';
            this._username = base._username;
            this._password = base._password;
            state = 'query';
          } else if ('#' == c) {
            this._host = base._host;
            this._port = base._port;
            this._path = base._path.slice();
            this._query = base._query;
            this._fragment = '#';
            this._username = base._username;
            this._password = base._password;
            state = 'fragment';
          } else {
            var nextC = input[cursor+1]
            var nextNextC = input[cursor+2]
            if (
              'file' != this._scheme || !ALPHA.test(c) ||
              (nextC != ':' && nextC != '|') ||
              (EOF != nextNextC && '/' != nextNextC && '\\' != nextNextC && '?' != nextNextC && '#' != nextNextC)) {
              this._host = base._host;
              this._port = base._port;
              this._username = base._username;
              this._password = base._password;
              this._path = base._path.slice();
              this._path.pop();
            }
            state = 'relative path';
            continue;
          }
          break;

        case 'relative slash':
          if ('/' == c || '\\' == c) {
            if ('\\' == c) {
              err('\\ is an invalid code point.');
            }
            if ('file' == this._scheme) {
              state = 'file host';
            } else {
              state = 'authority ignore slashes';
            }
          } else {
            if ('file' != this._scheme) {
              this._host = base._host;
              this._port = base._port;
              this._username = base._username;
              this._password = base._password;
            }
            state = 'relative path';
            continue;
          }
          break;

        case 'authority first slash':
          if ('/' == c) {
            state = 'authority second slash';
          } else {
            err("Expected '/', got: " + c);
            state = 'authority ignore slashes';
            continue;
          }
          break;

        case 'authority second slash':
          state = 'authority ignore slashes';
          if ('/' != c) {
            err("Expected '/', got: " + c);
            continue;
          }
          break;

        case 'authority ignore slashes':
          if ('/' != c && '\\' != c) {
            state = 'authority';
            continue;
          } else {
            err('Expected authority, got: ' + c);
          }
          break;

        case 'authority':
          if ('@' == c) {
            if (seenAt) {
              err('@ already seen.');
              buffer += '%40';
            }
            seenAt = true;
            for (var i = 0; i < buffer.length; i++) {
              var cp = buffer[i];
              if ('\t' == cp || '\n' == cp || '\r' == cp) {
                err('Invalid whitespace in authority.');
                continue;
              }
              // XXX check URL code points
              if (':' == cp && null === this._password) {
                this._password = '';
                continue;
              }
              var tempC = percentEscape(cp);
              (null !== this._password) ? this._password += tempC : this._username += tempC;
            }
            buffer = '';
          } else if (EOF == c || '/' == c || '\\' == c || '?' == c || '#' == c) {
            cursor -= buffer.length;
            buffer = '';
            state = 'host';
            continue;
          } else {
            buffer += c;
          }
          break;

        case 'file host':
          if (EOF == c || '/' == c || '\\' == c || '?' == c || '#' == c) {
            if (buffer.length == 2 && ALPHA.test(buffer[0]) && (buffer[1] == ':' || buffer[1] == '|')) {
              state = 'relative path';
            } else if (buffer.length == 0) {
              state = 'relative path start';
            } else {
              this._host = IDNAToASCII.call(this, buffer);
              buffer = '';
              state = 'relative path start';
            }
            continue;
          } else if ('\t' == c || '\n' == c || '\r' == c) {
            err('Invalid whitespace in file host.');
          } else {
            buffer += c;
          }
          break;

        case 'host':
        case 'hostname':
          if (':' == c && !seenBracket) {
            // XXX host parsing
            this._host = IDNAToASCII.call(this, buffer);
            buffer = '';
            state = 'port';
            if ('hostname' == stateOverride) {
              break loop;
            }
          } else if (EOF == c || '/' == c || '\\' == c || '?' == c || '#' == c) {
            this._host = IDNAToASCII.call(this, buffer);
            buffer = '';
            state = 'relative path start';
            if (stateOverride) {
              break loop;
            }
            continue;
          } else if ('\t' != c && '\n' != c && '\r' != c) {
            if ('[' == c) {
              seenBracket = true;
            } else if (']' == c) {
              seenBracket = false;
            }
            buffer += c;
          } else {
            err('Invalid code point in host/hostname: ' + c);
          }
          break;

        case 'port':
          if (/[0-9]/.test(c)) {
            buffer += c;
          } else if (EOF == c || '/' == c || '\\' == c || '?' == c || '#' == c || stateOverride) {
            if ('' != buffer) {
              var temp = parseInt(buffer, 10);
              if (temp != relative[this._scheme]) {
                this._port = temp + '';
              }
              buffer = '';
            }
            if (stateOverride) {
              break loop;
            }
            state = 'relative path start';
            continue;
          } else if ('\t' == c || '\n' == c || '\r' == c) {
            err('Invalid code point in port: ' + c);
          } else {
            invalid.call(this);
          }
          break;

        case 'relative path start':
          if ('\\' == c)
            err("'\\' not allowed in path.");
          state = 'relative path';
          if ('/' != c && '\\' != c) {
            continue;
          }
          break;

        case 'relative path':
          if (EOF == c || '/' == c || '\\' == c || (!stateOverride && ('?' == c || '#' == c))) {
            if ('\\' == c) {
              err('\\ not allowed in relative path.');
            }
            var tmp;
            if (tmp = relativePathDotMapping[buffer.toLowerCase()]) {
              buffer = tmp;
            }
            if ('..' == buffer) {
              this._path.pop();
              if ('/' != c && '\\' != c) {
                this._path.push('');
              }
            } else if ('.' == buffer && '/' != c && '\\' != c) {
              this._path.push('');
            } else if ('.' != buffer) {
              if ('file' == this._scheme && this._path.length == 0 && buffer.length == 2 && ALPHA.test(buffer[0]) && buffer[1] == '|') {
                buffer = buffer[0] + ':';
              }
              this._path.push(buffer);
            }
            buffer = '';
            if ('?' == c) {
              this._query = '?';
              state = 'query';
            } else if ('#' == c) {
              this._fragment = '#';
              state = 'fragment';
            }
          } else if ('\t' != c && '\n' != c && '\r' != c) {
            buffer += percentEscape(c);
          }
          break;

        case 'query':
          if (!stateOverride && '#' == c) {
            this._fragment = '#';
            state = 'fragment';
          } else if (EOF != c && '\t' != c && '\n' != c && '\r' != c) {
            this._query += percentEscapeQuery(c);
          }
          break;

        case 'fragment':
          if (EOF != c && '\t' != c && '\n' != c && '\r' != c) {
            this._fragment += c;
          }
          break;
      }

      cursor++;
    }
  }

  function clear() {
    this._scheme = '';
    this._schemeData = '';
    this._username = '';
    this._password = null;
    this._host = '';
    this._port = '';
    this._path = [];
    this._query = '';
    this._fragment = '';
    this._isInvalid = false;
    this._isRelative = false;
  }

  // Does not process domain names or IP addresses.
  // Does not handle encoding for the query parameter.
  /**
   * @constructor
   * @extends {URL}
   * @param {!string} url
   * @param {(URL|string)=} base
   */
  function jURL(url, base /* , encoding */) {
    if (base !== undefined && !(base instanceof jURL))
      base = new jURL(String(base));

    this._url = '' + url;
    clear.call(this);

    var input = this._url.replace(/^[ \t\r\n\f]+|[ \t\r\n\f]+$/g, '');
    // encoding = encoding || 'utf-8'

    parse.call(this, input, null, base);
  }

  jURL.prototype = {
    toString: function() {
      return this.href;
    },
    get href() {
      if (this._isInvalid)
        return this._url;

      var authority = '';
      if ('' != this._username || null != this._password) {
        authority = this._username +
            (null != this._password ? ':' + this._password : '') + '@';
      }

      return this.protocol +
          (this._isRelative ? '//' + authority + this.host : '') +
          this.pathname + this._query + this._fragment;
    },
    set href(href) {
      clear.call(this);
      parse.call(this, href);
    },

    get protocol() {
      return this._scheme + ':';
    },
    set protocol(protocol) {
      if (this._isInvalid)
        return;
      parse.call(this, protocol + ':', 'scheme start');
    },

    get host() {
      return this._isInvalid ? '' : this._port ?
          this._host + ':' + this._port : this._host;
    },
    set host(host) {
      if (this._isInvalid || !this._isRelative)
        return;
      parse.call(this, host, 'host');
    },

    get hostname() {
      return this._host;
    },
    set hostname(hostname) {
      if (this._isInvalid || !this._isRelative)
        return;
      parse.call(this, hostname, 'hostname');
    },

    get port() {
      return this._port;
    },
    set port(port) {
      if (this._isInvalid || !this._isRelative)
        return;
      parse.call(this, port, 'port');
    },

    get pathname() {
      return this._isInvalid ? '' : this._isRelative ?
          '/' + this._path.join('/') : this._schemeData;
    },
    set pathname(pathname) {
      if (this._isInvalid || !this._isRelative)
        return;
      this._path = [];
      parse.call(this, pathname, 'relative path start');
    },

    get search() {
      return this._isInvalid || !this._query || '?' == this._query ?
          '' : this._query;
    },
    set search(search) {
      if (this._isInvalid || !this._isRelative)
        return;
      this._query = '?';
      if ('?' == search[0])
        search = search.slice(1);
      parse.call(this, search, 'query');
    },

    get hash() {
      return this._isInvalid || !this._fragment || '#' == this._fragment ?
          '' : this._fragment;
    },
    set hash(hash) {
      if (this._isInvalid)
        return;
      if(!hash) {
        this._fragment = '';
        return;
      } 
      this._fragment = '#';
      if ('#' == hash[0])
        hash = hash.slice(1);
      parse.call(this, hash, 'fragment');
    },

    get origin() {
      var host;
      if (this._isInvalid || !this._scheme) {
        return '';
      }
      // javascript: Gecko returns String(""), WebKit/Blink String("null")
      // Gecko throws error for "data://"
      // data: Gecko returns "", Blink returns "data://", WebKit returns "null"
      // Gecko returns String("") for file: mailto:
      // WebKit/Blink returns String("SCHEME://") for file: mailto:
      switch (this._scheme) {
        case 'data':
        case 'file':
        case 'javascript':
        case 'mailto':
          return 'null';
      }
      host = this.host;
      if (!host) {
        return '';
      }
      return this._scheme + '://' + host;
    }
  };

  // Copy over the static methods
  var OriginalURL = scope.URL;
  if (OriginalURL) {
    jURL['createObjectURL'] = function(blob) {
      // IE extension allows a second optional options argument.
      // http://msdn.microsoft.com/en-us/library/ie/hh772302(v=vs.85).aspx
      return OriginalURL.createObjectURL.apply(OriginalURL, arguments);
    };
    jURL['revokeObjectURL'] = function(url) {
      OriginalURL.revokeObjectURL(url);
    };
  }

  scope.URL = jURL;

})(window);