drupal.js

/**
 * Parse the user ID from the Drupal.visitor.user.uid cookie.
 *
 * @return Number
 *   The user id: nonzero if it is an authenticated user, zero if it is the
 *   anonymous user, in which case the Drupal.visitor.user.uid cookie value will
 *   not exist either.
 *
 * @see user_user_login()
 * @see user_user_logout()
 */
Drupal.getUserID = function () {
  var userID;

  function parseUserID () {
    var values = document.cookie.split(';');
    for (var i = 0; i < values.length; i++) {
      var parts = values[i].trim().split('=');
      if (parts[0] === 'Drupal.visitor.user.uid') {
        return parseInt(parts[1], 10);
      }
    }
    return 0;
  }

  if (userID === undefined) {
    userID = parseUserID();
  }

  return userID;
};