JavaScript polyfill/shim for URLSearchParams. URLSearchParams provides utility methods for working with the query string portion of a URL.

/*!
Copyright (C) 2015-2017 Andrea Giammarchi - @WebReflection

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
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The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

Source:
https://raw.githubusercontent.com/WebReflection/url-search-params/master/build/url-search-params.max.js
*/
var URLSearchParams = URLSearchParams || (function () {
'use strict';

function URLSearchParams(query) {
  var
    index, key, value,
    pairs, i, length,
    dict = Object.create(null)
  ;
  this[secret] = dict;
  if (!query) return;
  if (typeof query === 'string') {
    if (query.charAt(0) === '?') {
      query = query.slice(1);
    }
    for (
      pairs = query.split('&'),
      i = 0,
      length = pairs.length; i < length; i++
    ) {
      value = pairs[i];
      index = value.indexOf('=');
      if (-1 < index) {
        appendTo(
          dict,
          decode(value.slice(0, index)),
          decode(value.slice(index + 1))
        );
      } else if (value.length){
        appendTo(
          dict,
          decode(value),
          ''
        );
      }
    }
  } else {
    if (isArray(query)) {
      for (
        i = 0,
        length = query.length; i < length; i++
      ) {
        value = query[i];
        appendTo(dict, value[0], value[1]);
      }
    } else {
      for (key in query) {
         appendTo(dict, key, query[key]);
      }
    }
  }
}

var
  isArray = Array.isArray,
  URLSearchParamsProto = URLSearchParams.prototype,
  find = /[!'\(\)~]|%20|%00/g,
  plus = /\+/g,
  replace = {
    '!': '%21',
    "'": '%27',
    '(': '%28',
    ')': '%29',
    '~': '%7E',
    '%20': '+',
    '%00': '\x00'
  },
  replacer = function (match) {
    return replace[match];
  },
  secret = '__URLSearchParams__:' + Math.random()
;

function appendTo(dict, name, value) {
  if (name in dict) {
    dict[name].push('' + value);
  } else {
    dict[name] = isArray(value) ? value : ['' + value];
  }
}

function decode(str) {
  return decodeURIComponent(str.replace(plus, ' '));
}

function encode(str) {
  return encodeURIComponent(str).replace(find, replacer);
}

URLSearchParamsProto.append = function append(name, value) {
  appendTo(this[secret], name, value);
};

URLSearchParamsProto.delete = function del(name) {
  delete this[secret][name];
};

URLSearchParamsProto.get = function get(name) {
  var dict = this[secret];
  return name in dict ? dict[name][0] : null;
};

URLSearchParamsProto.getAll = function getAll(name) {
  var dict = this[secret];
  return name in dict ? dict[name].slice(0) : [];
};

URLSearchParamsProto.has = function has(name) {
  return name in this[secret];
};

URLSearchParamsProto.set = function set(name, value) {
  this[secret][name] = ['' + value];
};

URLSearchParamsProto.forEach = function forEach(callback, thisArg) {
  var dict = this[secret];
  Object.getOwnPropertyNames(dict).forEach(function(name) {
    dict[name].forEach(function(value) {
      callback.call(thisArg, value, name, this);
    }, this);
  }, this);
};

/*
URLSearchParamsProto.toBody = function() {
  return new Blob(
    [this.toString()],
    {type: 'application/x-www-form-urlencoded'}
  );
};
*/

URLSearchParamsProto.toJSON = function toJSON() {
  return {};
};

URLSearchParamsProto.toString = function toString() {
  var dict = this[secret], query = [], i, key, name, value;
  for (key in dict) {
    name = encode(key);
    for (
      i = 0,
      value = dict[key];
      i < value.length; i++
    ) {
      query.push(name + '=' + encode(value[i]));
    }
  }
  return query.join('&');
};
var
  dP = Object.defineProperty,
  gOPD = Object.getOwnPropertyDescriptor,
  createSearchParamsPollute = function (search) {
    /*jshint validthis:true */
    function append(name, value) {
      URLSearchParamsProto.append.call(this, name, value);
      name = this.toString();
      search.set.call(this._usp, name ? ('?' + name) : '');
    }
    function del(name) {
      URLSearchParamsProto.delete.call(this, name);
      name = this.toString();
      search.set.call(this._usp, name ? ('?' + name) : '');
    }
    function set(name, value) {
      URLSearchParamsProto.set.call(this, name, value);
      name = this.toString();
      search.set.call(this._usp, name ? ('?' + name) : '');
    }
    return function (sp, value) {
      sp.append = append;
      sp.delete = del;
      sp.set = set;
      return dP(sp, '_usp', {
        configurable: true,
        writable: true,
        value: value
      });
    };
  },
  createSearchParamsCreate = function (polluteSearchParams) {
    return function (obj, sp) {
      dP(
        obj, '_searchParams', {
          configurable: true,
          writable: true,
          value: polluteSearchParams(sp, obj)
        }
      );
      return sp;
    };
  },
  updateSearchParams = function (sp) {
    var append = sp.append;
    sp.append = URLSearchParamsProto.append;
    URLSearchParams.call(sp, sp._usp.search.slice(1));
    sp.append = append;
  },
  verifySearchParams = function (obj, Class) {
    if (!(obj instanceof Class)) throw new TypeError(
      "'searchParams' accessed on an object that " +
      "does not implement interface " + Class.name
    );
  },
  upgradeClass = function(Class){
    var
      ClassProto = Class.prototype,
      searchParams = gOPD(ClassProto, 'searchParams'),
      href = gOPD(ClassProto, 'href'),
      search = gOPD(ClassProto, 'search'),
      createSearchParams
    ;
    if (!searchParams && search && search.set) {
      createSearchParams = createSearchParamsCreate(
        createSearchParamsPollute(search)
      );
      Object.defineProperties(
        ClassProto,
        {
          href: {
            get: function () {
              return href.get.call(this);
            },
            set: function (value) {
              var sp = this._searchParams;
              href.set.call(this, value);
              if (sp) updateSearchParams(sp);
            }
          },
          search: {
            get: function () {
              return search.get.call(this);
            },
            set: function (value) {
              var sp = this._searchParams;
              search.set.call(this, value);
              if (sp) updateSearchParams(sp);
            }
          },
          searchParams: {
            get: function () {
              verifySearchParams(this, Class);
              return this._searchParams || createSearchParams(
                this,
                new URLSearchParams(this.search.slice(1))
              );
            },
            set: function (sp) {
              verifySearchParams(this, Class);
              createSearchParams(this, sp);
            }
          }
        }
      );
    }

  }
;
upgradeClass(HTMLAnchorElement);
if (/^function|object$/.test(typeof URL) && URL.prototype) upgradeClass(URL);

/*

function spUpdate(a) {
  var
    search = this.toString(),
    password = a.password,
    username = a.username
  ;
  a.href = ''.concat(
    a.protocol, '//',
    username,
    password ? (':' + password) : '',
    username ? '@' : '',
    a.host,
    a.pathname,
    search ? ('?' + search) : '',
    a.hash
  );
}

*/

return URLSearchParams;
}());
(function (URLSearchParamsProto) {

  var iterable = (function () {
    try {
      return !!Symbol.iterator;
    } catch(error) {
      return false;
    }
  }());

  // mostly related to issue #24
  if (!('forEach' in URLSearchParamsProto)) {
    URLSearchParamsProto.forEach = function forEach(callback, thisArg) {
      var names = Object.create(null);
      this.toString()
          .replace(/=[\s\S]*?(?:&|$)/g, '=')
          .split('=')
          .forEach(function (name) {
            if (!name.length || name in names) return;
            (names[name] = this.getAll(name)).forEach(function(value) {
              callback.call(thisArg, value, name, this);
            }, this);
          }, this);
    };
  }

  if (!('keys' in URLSearchParamsProto)) {
    URLSearchParamsProto.keys = function keys() {
      var items = [];
      this.forEach(function(value, name) { items.push(name); });
      var iterator = {
        next: function() {
          var value = items.shift();
          return {done: value === undefined, value: value};
        }
      };

      if (iterable) {
        iterator[Symbol.iterator] = function() {
          return iterator;
        };
      }

      return iterator;
    };
  }

  if (!('values' in URLSearchParamsProto)) {
    URLSearchParamsProto.values = function values() {
      var items = [];
      this.forEach(function(value) { items.push(value); });
      var iterator = {
        next: function() {
          var value = items.shift();
          return {done: value === undefined, value: value};
        }
      };

      if (iterable) {
        iterator[Symbol.iterator] = function() {
          return iterator;
        };
      }

      return iterator;
    };
  }

  if (!('entries' in URLSearchParamsProto)) {
    URLSearchParamsProto.entries = function entries() {
      var items = [];
      this.forEach(function(value, name) { items.push([name, value]); });
      var iterator = {
        next: function() {
          var value = items.shift();
          return {done: value === undefined, value: value};
        }
      };

      if (iterable) {
        iterator[Symbol.iterator] = function() {
          return iterator;
        };
      }

      return iterator;
    };
  }

  if (iterable && !(Symbol.iterator in URLSearchParamsProto)) {
    URLSearchParamsProto[Symbol.iterator] = URLSearchParamsProto.entries;
  }

  if (!('sort' in URLSearchParamsProto)) {
    URLSearchParamsProto.sort = function sort() {
      var
        entries = this.entries(),
        entry = entries.next(),
        done = entry.done,
        keys = [],
        values = Object.create(null),
        i, key, value
      ;
      while (!done) {
        value = entry.value;
        key = value[0];
        keys.push(key);
        if (!(key in values)) {
          values[key] = [];
        }
        values[key].push(value[1]);
        entry = entries.next();
        done = entry.done;
      }
      // not the champion in efficiency
      // but these two bits just do the job
      keys.sort();
      for (i = 0; i < keys.length; i++) {
        this.delete(keys[i]);
      }
      for (i = 0; i < keys.length; i++) {
        key = keys[i];
        this.append(key, values[key].shift());
      }
    };
  }

}(URLSearchParams.prototype));