bookmarklet-cookie-feature-toggle.js

(function(){
  var featureKey = 'featureToggle';

  function get(key) {
    var cookies = document.cookie.split('; ');

    for (var i = 0, l = cookies.length; i < l; i++) {
      if (key === cookies[i].split('=').shift()) {
        return true;
      }
    }
  }

  if (get(featureKey)) {
    document.cookie = featureKey + '=0; path=/; max-age=1;';
  } else {
    document.cookie = featureKey + '=1; path=/;';
  }
  document.location.reload();
}());