Defer Parsing Of Javascript

Defer Parsing Of Javascript: To Improve Your Web Page Loading Speed

Defer Parsing Of Javascript

Did you ever test your website through a page speed testing tool and then end up being met with a recommendation/warning instruction to defer parsing of JavaScript in WordPress?

The warning can become a bit challenging to understand. This post explains what is it and ways to implement this on your website. Implementing it has a positive effect on your site’s web page load times. It is specifically very helpful for mobile visitors.


When JavaScript snippets are unnecessary for loading the critical route of a website, deferring it helps improve initial web page load time. This implies that the necessary content files to display the web page will receive loading priority over JavaScript snippets. It doesn’t have to be executed instantly. Because of the increasing need for page load speed, loading above-the-fold articles should be prioritized. It is usually what it really helps to achieve.

There are many reasons why we prefer to do it in WordPress. The most crucial one is page speed score and overall performance. Generally, JavaScript is usually placed between your <head> </head> tags. When anyone requests your website on google, it loads the code throughout. This means that for those who have plenty of JavaScript or lengthy strings, it will require additional time for the website’s content to appear. It is because it 1st waits for all your JavaScript to load.

By deferring parsing of JavaScript, the website would not await the JS code to load, which would lead to a quicker loading period. Nowadays, optimizing a site for the social press is very essential. Features such as Facebook, Twitter, Linkedin and other social networking sharing control keys/feeds make use of JavaScript. However, we should remember that content itself should get priority over others. Therefore by using it, we are able to greatly increase front-end user experience and SEO. In this WordPress tutorial, we cover several ways about how to do it in WordPress.

What is Defer Parsing of JavaScript in WordPress?

The perfect way to defer loading javascript means loading or parsing of javascript only begins after page content has been loaded. It means that it will not either affect page speed or the critical rendering path.

As told at the beginning of this post, If you’ve ever tested your web site via Google PageSpeed Insights, GTmetrix, or other page speed testing tool, you’ve probably run into the recommendation of it.

By accelerating your content’s above-the-fold load instances, your potential visitors may experience a speedier & responsive webpage.

Is defer loading JS an essential performance consideration?

when someone visits your WordPress site, your site’s server provides the webpage contents of your site in the visitor’s browser.

The visitor’s browser then starts at the very top and undergoes the code to render your website. While doing this, when ever it discovers any JavaScript, it’ll stop rendering all of those until it could fetch and parse the JavaScript document. And, It will do that for every script that it finds. It may have a negative impact on your site’s web page load times. Because of this, the visitor must stare at a blank display while their internet browser downloads and parses all of the JavaScript.

If a particular script isn’t essential to the core functioning of your website, you should prefer to do it. As you don’t want to buy time to block the way of loading more important elements of your site. Exactly, for this reason, page speed testing tools always recommend firmly to it.

Thus, your website will tell visitors’ browsers to hold back to download and/or parse JavaScript until after your site’s main content has finished loading. At that time, visitors can currently see and connect to your webpage. Therefore the wait instances to download and parse that JavaScript no more have such a poor effect on website/webpage.

Analyzing Your Website With Page Speed Testing Tools

To understand whether you should do it on your WordPress website, first you should analyze your website with an online page speed testing tool such as for example Pingdom, GTMetrix, Google PSI etc.


GTmetrix will provide you with a grade and in addition list out particular scripts that require to be deferred.

gtmetrix deferred parsing javascript

The common score for this suggestion in GTMetrix reaches at least 71%. Listed below are the outcomes after analyzing a web site.

The Different Solutions to Deferred Parsing of JavaScript

As we all know, There are many ways to defer parsing of JavaScript. Before we know about them, let’s understand about 2 attributes that you may use in your scripts:

  1. Async
  2. Defer

Both attributes permit visitor’s browsers to download JavaScript without pausing HTML parsing. below, you may find the difference between the two attributes.

With async attribute, it will not pause HTML parsing to fetch the script. It can pause the HTML parser to execute the script once it’s been fetched. It is the default behavior.

async attribute

With defer attribute, visitors’ browsers will still download the scripts while parsing the HTML. However, they will wait to parse the script until following the HTML parsing has been completed.

defer attribute

How to Defer Loading JavaScript in WordPress

There are primarily 3 different techniques to do it.  They are given below.

Defer Loading JavaScript via Plugin

It is one of the easiest and fastest ways to do it in WordPress. There are many WordPress plugins to pick from that will help defer parsing JavaScript. We’ll demonstrate how to do it with a few well-known plugins of WordPress.

To start, you will have to log in to your WordPress Dashboard and go to Plugins > Add New section.


There are several plugins to defer parsing javascript. Such as for example:

Choice 1.1 – WP Rocket Plugin

wp rocket

It is #1 plugin in this category. It has a bunch of performance optimization options. Also, WP Rocket will help you defer the parsing of JavaScript in the File Optimization tab of the WP Rocket dashboard. Search for the Load JavaScript deferred choice in the JavaScript Documents section of WP Rocket.

Just like the Async JavaScript plugin, WP Rocket also enables you to exclude jQuery in order to avoid problems with your website’s content:

Deferred Loading JavaScript

Choice 1.2 – Autoptimize Plugin


Choice 1.3 – Async JavaScript

Async Javascript defers or async javascript to WordPress what loads via wp_enqueue_script function. You don’t have to anything to configure to utilize this. Once you download, install and activate this plugin. Remaining things it will require care. Async JavaScript plugin allows defer or async characteristics to WordPress JavaScripts which loads via `wp_enqueue_script` function. The next attributes pressure JavaScript to load deferred or asynchronously, leading to faster web page load. To utilize it, you will just be required to set up and Activate the plugin.

Async JavaScript

Choice 1.4 – Speed Booster Pack

An alternative solution plugin with extra optimization techniques, such as for example query string removal, more and loading JS from Google Libraries. To begin, Activate the plugin and install it.

Speed Booster Pack ⚡ PageSpeed & Performance Optimization

Next, navigate to your WordPress Dashboard, select Settings and enter Rate Booster Pack.

Tick the box close to Defer Parsing of Javascript Data files and Save Adjustments to apply it.

speed booster settings

Choice 1.5 – WP Deferred JavaScript

This is an excellent plugin to defer loading javascript on WordPress. Just install and activate this plugin. It’ll automatically defer loading javascript as mentioned. A light-weight and incredibly easy-to-use plugin. You is only going to have to install and Activate it.

WP Deferred JavaScripts

Deferring parsing of JavaScript via functions.php

Alternatively, you can edit WordPress core files like functions.php to defer parsing of JS. For this approach, you don’t need to install plugin.  You yourself add the defer attribute to your JavaScript files. In order to achieve Defer Loading JavaScript, below-given code must be copied to underneath of your theme’s functions.php file

Though It’s fast and simple, but it doesn’t provide you the granular degree of control that plugins like Async JavaScript give.

defer loading javascript via functions.php

Note, You may download code of above from here.

Essentially, this snippet tells WordPress to include the defer attribute to all of your JavaScript files except jQuery.js.

Use Varvy’s Recommended Technique (Code)

Apart from it, Patrick Sexton of Varvy recommended a very good approach to defer loading JS. It runs on the script to contact an external JavaScript document. It is done only following the initial web page load is completed. This implies that visitor’s browsers won’t download or execute any JavaScript before the initial web page load is finished.

Or, you can include below code snippet to child theme’s functions.php file to automatically defer loading java scripts.

The Tricky Part of it is, this code snippet waits to both download and executes JavaScript until after your website completes its initial web page load. You need to add the script to your theme immediately prior to the closing </body> tag.

Script to call external javascript file

Note, You may download code of above from Varvy Code

Make sure to substitute “deferJS.js” with the actual document name/route of the JavaScript document you want to defer. Later, you may use the wp_footer hook to inject the code via your child theme’s functions.php file.

With this approach, you may wrap Varvy’s code in something similar to below snippet:

Defer parsing JavaScript with code snippet from Varvy
add_actions( ‘wp_footer’, ‘my_footer_scripts’ );
function my_footer_scripts(){

Move JavaScript to underneath of webpage

Finally, another approach that you’ll see is to move your JS to underneath of the webpage. Nevertheless, this method isn’t an excellent solution. It is because, despite the fact that your web page will be visible sooner in the browser, visitor’s browsers will still screen the web page as loading until all of the scripts finish. This may give the impression that the web page isn’t fully loaded.

Testing the changes

Once you’ve followed the above strategies to defer parsing JavaScript in WordPress, please follow the below procedure.

Check thoroughly your site to ensure that deferring particular scripts hasn’t broken your webpages/website. Usually, this can generally happen with jQuery. Because of this, many plugins provide the option to exclude jQuery.js files. Nevertheless, it may happen with various other scripts too. So, Run your website through the GTmetrix testing tool again to ensure that your website is deferring as many scripts as possible. As you have excluded jQuery.js, you may not get a perfect score of the website. However, your score is much better than the initial testing of the website.

Listed below are the performance outcomes after deferring JavaScript parsing in WordPress:

gtmetrix result after defer loading javascript

Congratulations, by following above easy steps, you boosted your website’s performance for a quicker and better load time!


To be able to load a full page, the browser needs to parse the contents of most <script> tags, which adds more time to the web page load. By reducing the quantity of JavaScript had a need to render the web page, and deferring parsing of not needed JavaScript until it requires to become executed, you can decrease the initial load period of your page.

There are many techniques that can be utilized to defer parsing javaScript. The easiest and favored technique is to just Defer loading of JavaScript until it really is needed. Another technique is by using the <script async> attribute, which helps prevent parsing from blocking the original web page load by deferring it before the browser’s UI thread isn’t busy doing another thing.

In this post, we’ve learned how to enhance the speed and performance of your WordPress website by deferring parsing of JavaScript. Keep in mind, the quicker and smoother your website is, the increased traffic and happier site visitors you will have! Further, Deferring the parsing of JavaScript on the WordPress website is normally an essential performance consideration.

Defer Parsing Of Javascript: To Improve Your WebPage Loading Speed