function QueryString() {
  this.queryString = window.location.search.substring(1);
  
  this.get = function(key) {
    var vars = this.queryString.split('&');

    for (var i=0;i<vars.length;i++) {
      var pair = vars[i].split('=');
      if (pair[0] == key) {
        return pair[1];
      }
    }
    return null;
  }
}