getDOMAttribute(attr) {
    var system = this.systems[attr];
    if (system) {
      return system.data;
    }
    return _a_entity_js__WEBPACK_IMPORTED_MODULE_7__.AEntity.prototype.getDOMAttribute.call(this, attr);
  }
Wraps Entity.getDOMAttribute to take into account for systems.
If system exists, then return system data rather than possible component data.