Optimizely: Persist custom attributes in a cookie

code.js

/**
 * Persist custom attributes via a cookie
 *
 * @param {string} COOKIE_DOMAIN
 *        The value of the `domain` attribute of the cookie.
 *        This should probably be the highest-level domain of your
 *        site (e.g., For 'blog.example.co.uk', use 'example.co.uk').
 */
var AttributePersistor = (function() {
  /**
   * SET PARAMETERS HERE
   */
  var COOKIE_DOMAIN = 'yourcookiedomain.com';
  // For maximum compatibility with browsers which implement an
  // old version of the cookie spec.
  COOKIE_DOMAIN = ensureLeadingDot(COOKIE_DOMAIN);

  var CUSTOM_ATTR_COOKIE_NAME = 'optimizelyCorsAttrs';

  /**
   * @param {string} str
   * @returns {string}
   *        The given string, modified to surely have a leading period.
   * @private
   */
  function ensureLeadingDot(str) {
    return (str[0] === '.') ? str : ('.' + str);
  }

  /**
   * @param {string} cookieValue
   *        Value to be assigned directly to the attributes cookie.
   * @private
   */
  function setCookie(cookieValue) {
    var expDate = (new Date()).setYear(2099);

    document.cookie =
      CUSTOM_ATTR_COOKIE_NAME + '=' + cookieValue +
      ';expires=' + expDate +
      ';domain=' + COOKIE_DOMAIN +
      ';path=/';
  }

  /**
   * @returns {(string|undefined)}
   *        The raw value of the attributes cookie.
   * @private
   */
  function getCookie() {
    var match = document.cookie.match(CUSTOM_ATTR_COOKIE_NAME + '=([^;]*)');
    return match ? match[1] : (void 0);
  }

  /**
   * @returns {Object.<string, (string|number)>}
   *        The attributes map currently stored in the cookie, deserialized.
   *        An empty object if the cookie is not set or isn't valid JSON.
   */
  function getAttributesFromCookie() {
    try {
      return JSON.parse(getCookie());
    } catch (e) {
      return {};
    }
  }

  /**
   * @param {Object.<string, (string|number)>} attributesToMerge
   *        A map of attributes to be merged into the map
   *        stored in the cookie.
   */
  function persistAttributes(attributesToMerge) {
    var merged = Object.assign({}, getAttributesFromCookie(), attributesToMerge);
    setCookie(JSON.stringify(merged));
  }

  /**
   * @param {Object} item
   * @returns {boolean}
   *        True if and only if the object resembles a request to the
   *        `User` JS API containing an attributes payload.
   */
  function isUserApiPayload(item) {
    return item instanceof Object &&
      item.type === 'user' &&
      item.attributes instanceof Object;
  }

  return {
    getAttributesFromCookie: getAttributesFromCookie,
    persistAttributes: persistAttributes,
    isUserApiPayload: isUserApiPayload,
  };
})();

window.optimizely = window.optimizely || [];

window.optimizely.push({
  type: 'addListener',
  filter: {
    type: 'lifecycle',
    name: 'initialized',
  },
  handler: function attributePersistorInitializedHandler(event) {
    // Merge the attributes stored in the cookie into the snippet's visitor profile
    window.optimizely.push({
      type: 'user',
      attributes: AttributePersistor.getAttributesFromCookie(),
    });
  },
});

window.optimizely.push({
  type: 'addListener',
  filter: {
    type: 'lifecycle',
    name: 'activated',
  },
  handler: function attributePersistorActivatedHandler(event) {
    // Write any attributes that the snippet read from pre-pushed User API
    // calls and from this origin's localStorage back into the cookie
    var snippetAttributes = window.optimizely.get('visitor').custom || {};
    var attributeMap = {};
    for (var attr in snippetAttributes) {
      attributeMap[attr] = snippetAttributes[attr].value;
    }
    AttributePersistor.persistAttributes(attributeMap);

    // Shim optimizely.push to have a side effect of persisting any attributes pushed
    // via it post-initialization. This must occur after initialization, as that's
    // when the API becomes available to shim.
    var optlyPush = window.optimizely.push;
    Object.defineProperty(window.optimizely, 'push', {
      value: function() {
        optlyPush.apply(null, arguments);

        var item = arguments[0];
        if (AttributePersistor.isUserApiPayload(item)) {
          AttributePersistor.persistAttributes(item.attributes);
        }
      }
    });
  },
});