How to Defer Parsing of JavaScript in WordPress


There are a few reasons why we should defer parsing of JavaScript in WordPress. The most important one is speed and performance. Generally, JavaScript is placed between the <head> </head> tags. When opening a website, it loads the code from top to bottom. This means that if you have lots of JS or long strings, it will take more time for the website’s content to appear, as it first waits for all the JavaScript to load.

By deferring parsing of JavaScript, the website would not wait for the JS code to load, which would result in a quicker loading time. Nowadays, optimizing a website for social media is crucial. Such features as Facebook, Twitter, Google+, Linkedin and other social network sharing buttons or feeds use JavaScript. However, we must keep in mind that content should be the priority, meaning that by deferring parsing of JavaScript we can greatly increase front-end user experience and SEO ranking. In this WordPress tutorial, we will cover several ways on how to defer parsing of JavaScript in WordPress.

Deferring parsing of JavaScript via functions.php

Alternatively, it is possible to carry out the task by editing one of WordPress core files. To defer parsing of JS, this code should be copied to the bottom of your theme’s functions.php file:

function defer_parsing_of_js ( $url ) {
if ( FALSE === strpos( $url, '.js' ) ) return $url;
if ( strpos( $url, 'jquery.js' ) ) return $url;
return "$url' defer ";
add_filter( 'clean_url', 'defer_parsing_of_js', 11, 1 );

Testing the Changes

Once you’ve are finished with one of the above options, use the same website speed tool and test your website. Here are the performance results after deferring JavaScript parsing in WordPress:

Defer Parsing of Javascript WordPress success in GTMetrix website optimization score

Congratulations, by following these few easy steps, you have boosted your website’s performance for a quicker and better experience!


In this short guide, we have learned how to improve the speed and performance of your WordPress website by deferring parsing of JavaScript. Remember, the faster and smoother your site is, the more traffic and happier visitors you will have!