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How to Defer Parsing of JavaScript in WordPress (5 Methods)

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What is Defer Parsing (The concept explained in detail)

Defer parsing of JavaScript is a basic HTML command usually utilized to command the browser for a particular purpose. It is generally scripted in a parallel manner or after the page loads. It often proves to be a beneficial tool to bring organic traffic to the location because nobody likes slow speeds. It enables the content to load at the best possible levels. If it takes an extended time to load, it shows other content to the visitors

Defer Parsing of JavaScript: What does it mean in WordPress?

Suppose you hold the experience of running your WordPress site through the Google PageSpeed Insights or any other page speed utilities. In that case, you may have encountered the prompt to defer JavaScript parsing. However, the question remains – what does it stand for, and why is it an essential criterion for performance?

Usually, when people visit your WordPress site, the site’s server renders the website’s HTML content to the user’s browser. As a result, the browser begins at the top while processing the code as it renders your site. During the move from top to bottom, if it discovers any JavaScript, it ceases rendering the remaining page until the completion of the fetching and parsing of the JavaScript file.

Repetition of the same process with each script can produce a negative impact on the load times. The visitor has to wait as the browser is downloading and parsing the JavaScript and may leave because of that, resulting in a worsening bounce rate.

Suppose you consider a specific script not to be essential to the site’s core functioning. In that case, it is better to prevent it from loading the site’s critical parts – a significant reason why most page speed testing tools prompt you to defer parsing.

When you perform defer parsing, your site tells the visitor’s browsers to delay downloading or parsing JavaScript until the site’s main content finishes loading. By that stage, the visitors are already interacting with your page’s contents, resulting in eliminating a negative effect arising out of the wait times.

Speeding the content load times doesn’t just optimize the site as per Google’s algorithms but results in a much improved, speedy experience for those visiting the site. It may also have a positive effect on your conversions – clicks, leads, and sales. 

How does the web page or site work after opening?

  • There is a specific link for each website. After clicking a link or searching about any website, the user’s browser requests from the user’s server to open the selected content, and then the server shows the content.
  • The HTML content is received and checked by the user’s browser, and therefore, the next step is that the browser shows the display of content on the screen.
  • During the process, if a JavaScript file comes into formation, the user’s browser stops the page while loading and starts fetching it before parsing it.
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Benefits of Defer Parsing

Defer parsing has uncountable benefits, and it may not be possible to define all of them here. It helps within the SEO optimization process, which is the highest quality of the plugin. Improvement in SEO means the article is often reached a broader audience during a short time. 

Defer Parsing of JavaScript fastens up the loading time and generates massive organic traffic on sites without requiring extended time

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Methods of fixing Defer Parsing In WordPress

Many methods are available if you want to repair Defer Parsing of JavaScript problems in WordPress. 

We discuss several essential techniques here:


  1. Using Function.php file: One of the best methods of deferring parsing is to use the functions.php file. However, you need to have considerable skills for this method. 
  1. Using WordPress Plugins: Many WordPress plugins offer to defer parsing, and here, we will discuss some of them in detail.
  1. Using BionicWP Nitro: If you’re looking for a mix of efficiency and speed, BionicWP Nitro can provide both. 
  1. Using Varvy’s Method: You can edit the sites’ code directly using Varvy’s method. 
  1.  Defer JavaScript via functions.php tweaking: It’s one of the most straightforward methods that offers incredible ease compared to the other plugins.

What are the two main attributes?

There are two main attributes that you simply can increase the scripts that include Async and Defer. By using these attributes, visitors don’t need to pass HTML parsing; they can quickly download the JavaScript to their browser. There is a little bit of difference in both attributes. Both attributes let visitors’ browsers download JavaScript without pausing HTML parsing. However, the difference is that while async doesn’t pause HTML parsing to fetch the script (as the default behavior would), it pauses the HTML parser to execute the script once it fetches.

Async JavaScript is a free WordPress plugin that allows users to write promise-based code with no blockage of the execution thread. It was discovered by Frank Goossens, who is well known for making the Autoptimize plugin too. Async JavaScript Plugin is the most straightforward plugin to defer parsing Javascript. 

  • Install the plugin and then activate it by using WordPress.org.
  •  Go to the settings bar and for the configuration of the plugin, go to the Async JavaScript.
  • You can enable the plugin’s functionality from the top to choose from the two options; async and defer.
  • Remember these important points while processing through this method.

Points to Remember

  •  While downloading JavaScript, Async does not stop parsing through HTML, but afterward, it prevents the parsing when it has to execute the JavaScript.
  • On the other hand, Defer continues parsing HTML and waits for the execution until the HTML parsing finishes.

Availability of options in Async Java Plugin

There are many other options available in Async Java Plugin but learning how to use them properly is all you have to do. The plugins and themes are available in abundance, but you have to break the site’s core for using the Query. You can do so by deferring, but the best procedure is to exclude the Query. 

Additionally, you can also include or exclude some particular scrips. The addition of plugins and user-friendly themes is also a great option to generate organic traffic.

WordPress plugins offer unique optimization techniques and superior performance in comparison to others. We discuss one of them in the lines below.

If you’re unsure how to defer parsing on your own, you can depend on BionicWP Nitro to make this happen.  NitroPack is another plugin that offers defer parsing solutions efficiently. BionicWP’s loading functionality utilizes a unique implementation of the technology to achieve desirable optimization results. 

The code snippet is the method recommended by Patrick Sexton of Varvy. The process helps downloading and executing JavaScript until the loading of the page finishes.

You can execute this strategy via adjustment of the code snippet supplied by Varvy. Furthermore, you have to insert the script in the theme before closing the </body> tag. 

Then replace the “defer.js” tag with the JavaScript file (original filename), which needs deferring. The next step is the code injection by using the child theme’s function.php file.

The Vary’s code which comes into play for this purpose is given below:

<script type=”text/javascript”>

function downloadJSAtOnload() {

var element = document.createElement(“script”);

element.src = “defer.js”;


if (window.addEventListener)

window.addEventListener(“load”, downloadJSAtOnload, false);

else if (window.attachEvent)

window.attachEvent(“onload”, downloadJSAtOnload);

else window.onload = downloadJSAtOnload;</script>

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If the user does not want to use the plugin method, there is a solution – Tweaking. It is a quick and straightforward process but has no comparison to the features provided by Async JavaScript.You can add the defer attribute to JavaScript files, and there is no need to add any plugin for the procedure.

Importance of learning the process before using it

First, you’ve got to find out how to use this process before implementing it on your site because it’s not like the other methods we’ve previously discussed. You only need to consider what you’re doing and confirm that you simply are choosing correctly. Most importantly, inspect if you’ve placed the code snippet within the right place or not. 

Don’t change anything afterward.


Creating a child theme is easy.


You can also create the child theme if you want to ensure you’re making the right edits within the functions.php file. If you wish to edit anything, you can easily access and alter it. After creating the kid theme, paste the code snippet then you’re ready to save lots of it. You just have to add the above code snippet to the functions.php file.

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 )

Frequently Asked Questions

Here are some of the most frequently asked questions:

For fixing, you will have to add a few minor changes to your code. You have the option of either finding all scripts and adding the defer tag or installing a plugin does this automatically.

Javascript’s defer parsing is the procedure of commanding the website’s browser to load specific leave files after the page’s loading. It enables the user to view the page’s content much quicker than if the defer parsing is not there.

With Async Javascript content loads as a new connection of its own while running parallel to the other code that already exists. However, with Async, the browser develops a more recent processing thread that doesn’t result in the slowness of any downloads currently occurring while the Javascript downloads and executes. Alternatively, defer requests the browser to do the script parsing once the remaining content finishes downloading. It’s suitable for the speeds, but there’s a catch. It may result in issues with the content if it references the deferred script.

Wrapping Up

We hope that you found what you were looking for with the process of deferring JavaScrit parsing. The crux of the matter is, the parsing can be done via plugins and manual tweaks and carries numerous benefits for the site, including enhanced SEO, improved user experience, and quicker loading times. Therefore, you need to ensure the deference of as many scripts as possible to achieve the best possible performance. However, you cannot underscore the importance of keeping backups and consistent testing to ensure the correct scripts’ deference instead of the wrong ones. It may sound hectic and may add to the responsibilities, but the benefits and gains make it worth the effort. 

It is essential to carefully consider the process of deferring and parsing the JavaScript of your website. You can use any deferring method for parsing JavaScript in WordPress. But in any case, do remember to depend on experts to achieve the best speeds and avoid mishaps.

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