(function () {
  // 加载 gtag.js
  var script = document.createElement('script');
  script.async = true;
  script.src = '#';
  document.head.appendChild(script);

  // 初始化 dataLayer
  window.dataLayer = window.dataLayer || [];
  function gtag(){dataLayer.push(arguments);}
  window.gtag = gtag;

  // 配置 GA
  gtag('js', new Date());
  gtag('config', '');
})();