whole_func_string: function getId(callback) {
      var self = this;
      if (typeof self.params.IdentityId === 'string') return callback();
  
      self.cognito.getId(function(err, data) {
        if (!err && data.IdentityId) {
          self.params.IdentityId = data.IdentityId;
        }
        callback(err, data);
      });
    }
func_code_string: function getId(callback) {
      var self = this;
      if (typeof self.params.IdentityId === 'string') return callback();
  
      self.cognito.getId(function(err, data) {
        if (!err && data.IdentityId) {
          self.params.IdentityId = data.IdentityId;
        }
        callback(err, data);
      });
    }
func_documentation_string: Retrieves a Cognito ID, loading from cache if it was already retrieved
  on this device.
  
  @note If not loaded explicitly, the Cognito ID is loaded and stored in
  localStorage in the browser environment of a device.