While the JavaScript tracking snippet described above ensures the script will be loaded and executed asynchronously on all browsers, it has the disadvantage of not allowing modern browsers to preload the script.
The alternative async tracking snippet below adds support for preloading, which will provide a small performance boost on modern browsers, but can degrade to synchronous loading and execution on IE 9 and older mobile browsers that do not recognize the async script attribute. Only use this tracking snippet if your visitors primarily use modern browsers to access your site.
<!-- Google Analytics -->
<script>
window.ga=window.ga||function(){(ga.q=ga.q||[]).push(arguments)};ga.l=+new Date;
ga('create', 'UA-XXXXX-Y', 'auto');
ga('send', 'pageview');
</script>
<script async src='https://www.google-analytics.com/analytics.js'></script>
<!-- End Google Analytics -->