How and Why You Should Remove Unused JavaScript for Optimal Performance

June 17, 2024

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How and Why You Should Remove Unused JavaScript

There are multiple ways to clean up your website and improve its performance, and one effective method is removing unused JavaScript. JavaScript has been around for years and was created to make web applications more dynamic. In the world of web development, "dynamic" refers to the ability to change or update a website in real-time, often in response to user interactions.

This is where and why the removal of unused JavaScript becomes important. If done properly, removing unused JavaScript from your website can lead to many positive outcomes, such as improved user experience, higher performance and SEO scores, enhanced code quality, and much more. Let’s dive into detail on what JavaScript is, why it’s important to stay on top of it, and the benefits of removing it when not in use.

What is Unused JavaScript?

Before reviewing what unused JavaScript is, let's go over what JavaScript is. JavaScript, by definition, is an object-oriented computer programming language commonly used to create interactive effects within web browsers. JavaScript allows you to implement dynamic features onto your website that cannot be done with only HTML and CSS. A world without JavaScript means relying solely on HTML and CSS, which limits you to mainly static content.

A world without JavaScript is bland, uninteresting, and unengaging. But a world with too much JavaScript can surely slow us all down. This is where the term unused JavaScript originates. Unused JavaScript refers to portions of JavaScript code that are included in a web page or web application but are not executed or utilized during the page's operation. This code might be loaded into the browser, adding to the page's overall size and load time, but it does not contribute to the functionality or the user experience of the page.

Here’s a more detailed breakdown of what constitutes unused JavaScript:

  • Not Executed: This is when a piece of javascript is never called nor ran during the page's lifecycle. This can happen due to the code being obsolete, redundant, or included in an error.
  • Redundant or Deprecated: This includes older scripts that are no longer necessary in your site, this is normally a result of functionality has been replaced or deprecated by new code or updates.
  • Conditional Loading: JavaScript that is intended to execute under specific conditions that never occur for a user or for a specific page view might remain unused.
  • Leftover Code: During development, developers may write extra functions or scripts for testing purposes that are not removed or disabled in the production version of the website.
  • Unused Libraries: Entire libraries or parts of libraries may be included in the page but not actually used. For instance, including a large JavaScript library like jQuery without using any of its features in the page.
  • Dead Code: Code that might have been relevant to previous versions of a website or application but no longer serves any purpose in the current context.

Impact of Unused JavaScript

At first glance, unused JavaScript might not seem like a major concern for an eCommerce store. However, it can have a more detrimental effect on your online business than one might realize. Unused JavaScript can slow down page load times, frustrate users, and even harm your search engine rankings. Let’s discuss the negative impact unused JavaScript can have on your eCommerce store.

Increased Load Time

Unused JavaScript contributes significantly to the overall size of the JavaScript files that need to be downloaded. Larger files take more time to download, thereby increasing the initial load time of the website. Think of it like moving a house: a tiny one-bedroom house can be transported quickly and with minimal resources, while a large four-bedroom house takes much more time, effort, and resources to move. Similarly, a website with a small amount of necessary JavaScript loads swiftly, while one burdened with excessive, unused code takes longer.

Large JavaScript files are also more susceptible to network latency, especially on slower connections. This latency further delays the loading process, leading to a sluggish user experience. On a slow network, downloading and processing these unnecessary files can feel like a heavy burden, similar to the tiring process of transporting a large, unnecessary truckload across the country.

Here are a few of the many consequences of a slow eCommerce store:

Increased Bounce Rates: Fast site speed has certainly become a high expectation in eCommerce, and stores burdened with heavy, unused JavaScript definitely suffer from it. Slow-loading pages frustrate users, causing them to abandon the site before it fully loads. In fact, Google confirmed that the probability of a bounce increases by 32% as page load time goes from 1 second to 3 seconds.

Reduced Conversion Rates: Site speed sets the tone; think of it as a first impression, and if your site provides poor performance, where else does your brand poorly perform? This was shown in a study where nearly  70% of consumers admitted that page speed influences their likelihood to buy. Participants said they’re less likely to make a purchase (or even less likely to return in the future) if loading times were slower than expected. If you want visitors to buy your products, fast site speed is essential.

Lower Customer Retention: If you’ve ever been on a slow site, you know how annoying it is to be interested in a product but have to give up because it's taking forever to load. This experience doesn’t make you want to keep shopping or come back. That is why fast, seamless experiences encourage repeat visits, higher average order values (AOVs), and foster customer loyalty. Conversely, slow load times can deter customers from returning, impacting long-term customer loyalty and retention.

Poor User Experience: Unused JavaScript increases the time it takes for pages to become interactive, affecting how quickly users can engage with content, add items to their cart, or complete purchases. This can frustrate users and discourage them from exploring further. This is especially true for mobile users, who are affected by slow load times more than desktop users due to slower network speeds and less powerful devices. Unused JavaScript exacerbates these issues, leading to poor mobile shopping experiences and potentially lost sales.

SEO and Search Ranking Penalties

Every eCommerce store wants to be visible to potential buyers, but it can be challenging to climb the search engine rankings if your site is slowing you down. This is quite literal when it comes to Google, which considers page speed as a ranking factor. If your site has slow load times due to excessive JavaScript, you will rank lower in search results, reducing visibility and organic traffic.

This issue also affects crawl efficiency. Reduced crawl efficiency refers to the decreased ability of search engines to effectively crawl and index a website’s pages due to excessive or unnecessary content, leading to fewer pages being discovered and indexed. Because search engines allocate a limited budget for crawling pages, heavy, unused JavaScript can consume more of this budget, negatively impacting search engine optimization (SEO) efforts by reducing the number of pages that can be crawled and indexed, further impacting your store’s ranking and visibility.

Security and Maintenance Risks

Many people may not realize it, but unused JavaScript can create vulnerabilities that attackers could exploit.However, unused JavaScript can potentially expose vulnerabilities that attackers could exploit. Keeping the codebase lean and free of unnecessary scripts reduces the risk of security breaches.

Beyond the risk of a security breach, unused JavaScript can impact your website’s maintenance routine. By having a larger, more complex codebase with unused scripts, updates and maintenance can become more difficult, increasing the risk of introducing errors or bugs that could impact your site’s functionality.

Negative Impact on Analytics and Personalization

With today's technology, understanding your users and how they interact with your site is easier than ever. However, your site’s unused JavaScript could be setting you back from doing so. Here’s how: 

Delayed Data Collection:Unused JavaScript can slow down analytics scripts, leading to delayed or inaccurate data collection. This affects the site’s ability to track user behavior, make data-driven decisions, and ultimately impacts your store’s ability to improve.

Hindrance to Personalization: Unused JavaScript can hinder the implementation of personalization features, which can delay or even halt the provision of relevant product recommendations and improvements in user experience.

These issues are just a few of the many consequences of slow site speed. If your site suffers from slow performance, it may take more than removing unused JavaScript. To combat it quickly and effectively, consider working with Nostra. Our product suite drastically reduces latency, enhances page performance, and optimizes Core Web Vitals, freeing up your time to focus on broader business objectives.

How to Pinpoint Your Unused Javascript

Now that we’ve uncovered the negative impact of this silent performance killer, let’s discuss what options you have when it comes to finding your unused JavaScript within your website. This can prove difficult because there are thousands of files within your site. How can you know which ones are important versus those that are useless and slowing you down? The following tools can help you answer such questions:

Chrome DevTools

If you're looking for a quick and easy way to locate all of your unused JavaScript files, use  Google’s Chrome DevTool. DevTools diagnose site problems quickly, including JavaScript issues, helping you build better websites faster. To find your unused JavaScript files, use the following steps:

1. Open the DevTool.

2. Press “Ctrl/Command+Shift+I.”

3. Press “Ctrl/Command+Shift+P” to open the command menu.

4. Click on “Show Coverage.”

5. Reload the page again.

You have found all of your unused files.


Lighthouse, an open-source, automated tool for measuring the quality of web pages, is another practical tool that denotes every unused JavaScript file from your site’s code. To find your unused JavaScript, you'll want to do the following:

1. Once Lighthouse has finished analyzing your website, find a tab labeled as ‘Remove Unused JavaScript.’

2. Click on that tab, and you'll find the proper list.

PageSpeed Insights

Another easy-to-use tool for locating your site speed killers is PageSpeed Insights. This tool is also great for website optimization, helping you understand the ins and outs of your site and its visitors. To locate unused JavaScript files within your site, you have to go to the “Opportunities” section. There will be a segment named “Remove unused JavaScript.” Easy as pie.


GTmetrix has many mixed reviews, but if you are a fan, you’ll want to find a chart called the “waterfall chart.” In this chart, you’ll want to find the ‘JS’ tab. This is where you’ll find your unused files.

Using one of the previous tools mentioned will get you the information you need to begin cleaning out your unused JavaScript. Now that we understand the importance of removing your unused JavaScript, let's review the methods one can follow to remove it in these steps:

How to Remove Unused JavaScript

Follow these steps to properly remove or reduce your website's unused javascript:

1.)Detect Your Unused JavaScript

Refer to our previous discussion, any of the above methods can help you find and address your unused JavaScript.

2.)Prioritize Crucial Scripts

Before jumping straight into removing or reducing your unused JavaScript, it is important to identify which JavaScript files are vital for your website's functionality and performance. This can include scripts such as forms, navigation menus, or interactive elements. Once you’ve determined the crucial scripts within your site, be sure to highlight and prioritize not removing or modifying them during this process. A good practice is to remove JavaScript one by one and review your site to check for any unexpected behavior or errors that may arise after removing that piece of code.

Additionally, you can use automated testing tools such as Selenium or Cypress to ensure that any changes you make to your code do not break existing functionality.

3.) Minify Your JavaScript

Minification is the process of removing unnecessary whitespace, comments, and line breaks from your JavaScript files to reduce their size and improve loading times. For those who would like to avoid touching their site’s code, use code minifiers such as Google Closure Compiler or UglifyJS. These tools will go through your site’s code and do the job for you by removing any unnecessary whitespace and comments.

Another great technique for removing unwanted code is utilizing static code analysis tools such as SonarQube or Code Climate to detect any unused code and provide recommendations for how to remove it. Additionally, you can use automated testing tools such as Selenium or Cypress to ensure that any changes you make to your code do not break existing functionality.

5.) Code Refactoring

Code refactoring involves restructuring and cleaning up existing code without changing its external behavior, similar to the previous step but more advanced that removing spaces and comments. It is recommended that when attempting code refactoring it is best to leave it with someone with technical web experience. 

By refactoring your JavaScript code, you can remove redundant or unused scripts, making your codebase more efficient and easier to manage. This step is great for improving code readability, maintainability, and performance. Below is a summary of steps on how to refactor your code effectively:

Steps to Refactor Code Effectively:

1. Analyze Your Codebase: Use tools like ESLint or JSHint to analyze your JavaScript code and identify unused or redundant scripts.

2. Identify Redundant Code: Look for patterns or code blocks that are no longer in use or have been replaced by newer scripts.

3. Remove Unnecessary Code: Carefully remove or comment out the identified unused scripts to avoid breaking any existing functionality.

4. Test Thoroughly: Use automated testing tools like Selenium or Cypress to test your website and ensure that the removal of unused code does not introduce any new issues.

5. Document Changes: Keep a record of the changes made during the refactoring process for future reference and maintenance.

4.)Remove Unused Plugins

Plugins are great for providing your users with the user experience they deserve while saving you plenty of time on building your website. The only downside is that plugins can contribute a large share of unused code on a site. Therefore, we recommend uninstalling and deleting any plugins you’re not using. It's important to remember that plugins can be tricky, and even when you think you've removed them, sometimes you've only deactivated them, resulting in fragments of ghost code being left behind. Therefore, even if the code isn’t doing anything, it still takes time for browsers to download and process it. Ensure to delete the plugin files and run a quick test afterward to see if there are any fragments left behind.

5.) Ensure Consistent Monitoring and Post-Optimization Functionality

Optimization is a continuous journey. Unused JavaScript piles up like leaves in a garden, requiring regular attention to keep it neat and efficient. Staying diligent in clearing it out ensures a well-maintained and thriving environment.

During your removal of any script and afterward, you should regularly test your website on various browsers to ensure it is functioning smoothly and providing an ideal user experience. This can be done by keeping a continuous eye on all user interactions, navigation functionality, form submissions and inputs, dynamic content loading, and overall performance scores to ensure your site remains unaffected by its recent changes.

6.) Regular Maintenance

Optimization is not a one-time task. It’s an ongoing process. Periodically revisit your website’s JavaScript code to identify and remove new instances of unused code. Continuously monitor your website’s performance using tools and analytics to detect any emerging issues related to JavaScript efficiency. Here are a few WordPress maintenance plugins you should definitely check out.

By following this comprehensive process, you can effectively remove unused JavaScript from your website, improve its performance, and ensure that it continues to deliver a seamless user experience. Optimization should be integral to your website maintenance strategy to keep it running efficiently over time.

Best Practices and Tips for Future Javascript

If you successfully remove the unused JavaScript from your site, congratulations! However, before you start adding new features or content, consider these tips to prevent similar issues in the future:

  1. Prioritize Efficiency: Focus on writing clean, efficient code from the start. Keep your code modular and well-organized to make it easier to manage and update.
  2. Regularly Review Your Code: Schedule periodic code reviews to identify and eliminate any unnecessary scripts or features that may accumulate over time.
  3. Use Automated Tools: Implement tools that automatically detect and alert you to unused code, ensuring your site remains lean and efficient.
  4. Practice Continuous Integration: Adopt continuous integration practices to consistently test and validate your code, catching potential inefficiencies early in the development process.
  5. Document Your Changes: Maintain clear documentation of any changes you make to your codebase. This will help you track what has been added or removed and assist in future maintenance.

Incorporating these best practices and tips into your development workflow will help you maintain a clean, efficient, and high-performing website. Remember, optimization is an ongoing process. Staying diligent in removing unused JavaScript ensures that your site will run smoothly and efficiently for years to come, enhancing performance, user experience, SEO rankings, and security.

For those looking to achieve and guarantee all of these benefits quickly and effectively, consider partnering with Nostra. At Nostra, we specialize in optimizing website speed and performance overnight, freeing you up to focus on more significant business objectives. To learn more and see how we can help, book a demo with us today.

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