As would be expected, loading the JavaScript snippet in this way has a negative impact on the web performance of our website. It’s a trade-off we struggled with for a long time. Should we follow web performance best practices and load the Optimizely JavaScript asynchronously, or follow experimentation best practices and load it blocking as the first asset? Both of these approaches have their pros and cons.
In one of our web performance audit conversations, we decided to experiment with techniques to address the performance problem. Our first idea was to take Optimizely out of the <head> and/or put the async attribute on the <script> tag so that it does not block render and loads asynchronously. Our Product Management team pointed out the resulting edge side include (ESI) and
