What the google analytics tracking snippet really does...

snippet.js

// create a ga function in the window object (if not exists)
// which queues all function calls as long as the real script
// is not loaded yet
window.GoogleAnalyticsObject = 'ga';
window.ga = window.ga || function () {
  (window.ga.q = window.ga.q || []).push(arguments)
};
window.ga.l = 1 * new Date();

// create new script tag to load the "real" ga function
newScript = document.createElement('script');
newScript.async = 1;
newScript.src = 'https://www.google-analytics.com/analytics.js';

// insert the new script tag into the dom
firstScriptInHtml = document.getElementsByTagName('script')[0];
firstScriptInHtml.parentNode.insertBefore(newScript, firstScriptInHtml)