How to use the @lrnwebcomponents/haxcms-elements/lib/core/haxcms-site-store.js.store.activeItemFields function in @lrnwebcomponents/haxcms-elements

this.__disposer = autorun(() => {
      this.fields = toJS(store.activeItemFields);
    });
  }

autorun(reaction => {
        const fields = toJS(store.activeItemFields);
        this.hasImage = this._computeHasImage(fields);
        if (this.hasImage) {
          this.image = fields.images[0].src;
        }
        this.__disposer.push(reaction);
      });
    }, 0);