It’s really frustrating when you google to find something and have to scroll through a blog of affiliate link garbage to get the answer you are looking for.  So if you are trying to optimize your website and GTmetrix is telling you to “Defer parsing of JavaScript” here is a code you can try adding to your .htaccess file that could help.  Yes, there are plugins that exist that will load JavaScript deferred or will Async JavaScript, but I personally try to avoid additional plugins whenever possible.

function defer_parsing_of_js( $url ) {
    if ( is_user_logged_in() ) return $url; //don't break WP Admin
    if ( FALSE === strpos( $url, '.js' ) ) return $url;
    if ( strpos( $url, 'jquery.js' ) ) return $url;
    return str_replace( ' src', ' defer src', $url );
}
add_filter( 'script_loader_tag', 'defer_parsing_of_js', 10 );

Try adding this to your functions.php file.  Make sure you backup or have ftp access in case you have issues per usual.  I personally no longer use a standard backup, I originally had a wordpress multisite and had a hell of a time figuring out how to export a website from a multisite.  Here’s an affiliate link free tip, I found a plugin you can use temporarily called, Prime Mover, that makes it super easy to export a website from a wordpress multisite or migrate a wordpress website in general.  I have zero affiliation with them, I just am very grateful they exist.  It’s an excellent plugin because you can export your wordpress website from a wordpress website or individual directory and have a complete backup.  If something bad happens or you make a mistake, just install a fresh copy of WordPress, install the Prime Mover plugin, and bam, you’re back up and running like nothing happened.  Best of all, IT IS FREE!! 

A huge thank you to the Prime Mover developers! It’s quite a bit faster to use the premium feature and supports the developers if you are migrating multiple websites from a wordpress multisite but the free version still works beautifully and doubles as a backup.  I highly recommend them and will let you search for them yourself in the wordpress plugins so you know I’m not profiting off this endorsement.  I’m just a fan. 

If Google, GTmetrix, and/or Pingdom are giving you a laundry list of optimization for your WordPress website, do yourself a favor and just get WP Rocket, it’s one of the easiest and best caching plugins on the market and loaded with features for WordPress website optimization at a very low cost per year.  If you read this, take a chance with W3 Total Cache, and break your website, then please remember this, “I told you so!”