Google Analytics Launches Asynchronous Tracking- Google Developers Blog
Dec 1, 2009

Summary
Introduced asynchronous tracking for Google Analytics, allowing for non-blocking loading of the tracking code and improving page load performance. This change enables websites to load faster by not waiting for the analytics script to execute.
More from the Website Optimization and Experimentation APIs trail
- Introducing Autotrack for analytics.js- Google Developers Blog
- IISpeed accelerates visitnapavalley.com, with PageSpeed optimization by Google- Google Developers Blog
- Crawling the infinite scroll- Google Developers Blog
- Measuring network performance with Resource Timing API- Google Developers Blog
- Speeding up mobile pages with mod_pagespeed and ngx_pagespeed- Google Developers Blog