In a default WordPress installation, the robots.txt file does not exist in your web site’s root directory. WordPress dynamically generates robots.txt content for your web site when it receives a request for the robots.txt file. The technique shown in this article will modify the contents of WordPress’ dynamically generated robots.txt contents.
In this article, we will intercept the generation of script tags, and alter the output in an attempt to improve web site performance. The filter code will add either a defer or async attribute to the script tag.