http://url.spec.whatwg.org/ - thanks to Anne van Kesteren for the spec

URLSearchParams.js

"use strict";

function URLSearchParams(query) {
  var data = [];
  query = query.toString();
  query = query.replace(/\+/g, " ");
  var strings = query.split("&");
  var l = strings.length;
  var i = 0;
  while (i < l) {
    var s = strings[i];
    if (s !== "") {
      var j = s.indexOf("=");
      var name = s;
      var value = "";
      if (j !== -1) {
        name = s.slice(0, j);
        value = s.slice(j + 1);
      }
      name = decodeURIComponent(name);
      value = decodeURIComponent(value);
      data.push(name);
      data.push(value);
    }
    i += 1;
  }
  this.data = data;
}

URLSearchParams.prototype.get = function (name) {
  name = name.toString();
  var data = this.data;
  var l = data.length;
  var i = 0;
  while (i < l) {
    if (data[i] === name) {
      return data[i + 1];
    }
    i += 2;
  }
  return undefined;
};
URLSearchParams.prototype.getAll = function (name) {
  name = name.toString();
  var x = [];
  var data = this.data;
  var l = data.length;
  var i = 0;
  while (i < l) {
    if (data[i] === name) {
      x.push(data[i + 1]);
    }
    i += 2;
  }
  return x;
};
URLSearchParams.prototype.set = function (name, value) {
  name = name.toString();
  value = value.toString();
  var data = this.data;
  var l = data.length;
  var i = 0;
  while (i < l) {
    if (data[i] === name) {
      data[i + 1] = value;
      return;
    }
    i += 2;
  }
  data.push(name);
  data.push(value);
};
URLSearchParams.prototype.append = function (name, value) {
  name = name.toString();
  value = value.toString();
  var data = this.data;
  data.push(name);
  data.push(value);
};
URLSearchParams.prototype.has = function (name) {
  name = name.toString();
  var data = this.data;
  var l = data.length;
  var i = 0;
  while (i < l) {
    if (data[i] === name) {
      return true;
    }
    i += 2;
  }
  return false;
};
URLSearchParams.prototype["delete"] = function (name) {
  name = name.toString();
  var data = this.data;
  var l = data.length;
  var i = 0;
  var k = -1;
  while (i < l) {
    if (data[i] !== name) {
      k += 1;
      data[k] = data[i];
      k += 1;
      data[k] = data[i + 1];
    }
    i += 2;
  }
  data.length = k + 1;
};
URLSearchParams.prototype.toString = function () {
  var output = "";
  var data = this.data;
  var l = data.length;
  var i = 0;
  while (i < l) {
    output += (encodeURIComponent(data[i]));
    if (data[i + 1] !== "") {
      output += ("=");
      output += (encodeURIComponent(data[i + 1]));
    }
    output += "&";
    i += 2;
  }
  return output;
};