We have already stressed in previous posts the importance of the time it takes for a web page to be fully loaded in the client browser: users will get a better impression of the site if the content is “snappy”. Besides, the page load time is a factor that the major search engines, including Google, take into account in their ranking algorithms.
Downloading and processing external resources is often one of the main contributions to the total page load time. Among these resources, external javascript libraries and CSS stylesheets are most often the main contributors to this.
We have already covered in our previous post on “How to reduce the page load time with asynchronous javascript” the way to load javascript resources in parallel with the main HTML document, so as not to block the rendering of the above-the-fold content.
This post continues the series on web site optimization techniques, explaining how to load asynchronously external CSS stylesheets.