setEntityAttribute(attr, oldVal, newVal) {
    if (_component_js__WEBPACK_IMPORTED_MODULE_1__.components[attr] || this.components[attr]) {
      this.updateComponent(attr, newVal);
      return;
    }
    if (attr === 'mixin') {
      // Ignore if `<a-node>` code is just updating computed mixin in the DOM.
      if (newVal === this.computedMixinStr) {
        return;
      }
      this.mixinUpdate(newVal, oldVal);
    }
  }
Deals with updates on entity-specific attributes (i.e., components and mixins).

@param {string} attr
@param {string} oldVal
@param {string|object} newVal