How to reduce Unused JavaScript Code?

How to reduce unused JavaScript?

Ashkar Gomez
11min read
Table of Contents

Ever feel like that your website is fully optimized for search engines, but the ranking still remains unchanged?

The actual cause might lie within the code base and that is “Unused JavaScript”.

In the highly competitive field of Search Engine Optimization (SEO), where each click and conversion counts, improving the performance of the website is essential.

But the unused Javascript code in the website negatively impacts the website’s performance and user experience.

By eliminating the unnecessary JavaScript code and prioritizing speed, not only the website’s visibility gets increased but also rankings get skyrocketed in the Search Engine Results Page (SERP).

In this article, let us explore in detail the hidden potential of reducing unused JavaScript to enhance the SEO Strategy.

What is Unused JavaScript Code?

JavaScript code that appears on a webpage or web application but is not actively used or executed during the browsing session of the user is referred to as “unused JavaScript”.

This includes variables, functions, modules and entire scripts that are part of the codebase but are not invoked or accessed by any website functionality.

As developers add new features, modify existing code or integrate third party libraries into the website, there may be an accumulation of unused JavaScript.

Although the website’s functionality may not be directly impacted by this unused code, it can have several negative consequences such as slower page loads, decreased performance and unnecessary codebase complexity.

Finding and eliminating unnecessary JavaScript is crucial for enhancing user experience, speeding up development processes, and optimizing website performance.

Importance of reducing unused JavaScript code

Reducing unused JavaScript is extremely important for several reasons:

  • Decreases the Page load times resulting in faster and more responsive websites.
  • Enhances user experience and reduces bounce rates.
  • Increases the possibility of higher search rankings in Search Engine Results Page (SERP).
  • Reduce the bandwidth consumption and decrease server load which lowers the website hosting costs.
  • Minimize the chance of introducing bugs, speed up development and increase code maintainability.
  • Provides users a seamless experience across various devices and network conditions.
  • Improved accessibility and compatibility, enabling a larger number of users to visit and engage with the website without experiencing compatibility problems.

Common Sources of Unused JavaScript Code

Some of the common causes that leads to unused JavaScript are as follows:

  • Overloading of Code – Developers include more functionality than is required to handle edge cases or anticipated requirements. This results in some parts of the JavaScript codebase remaining unutilized.
  • Libraries and Dependencies from Third Party – Including third-party libraries or dependencies frequently results in extra functionality that might not be used to its full potential. This leads to unused JavaScript code from those libraries
  • Removing or altering a Feature – Features could be added, removed, or altered throughout the development process, making the JavaScript code outdated or unused.
  • Incomplete Reorganizing – Developers may leave behind unneeded code snippets or functions that were meant to be used but are now unnecessary when refactoring or optimizing code.
  • Paths for Conditional Code – Certain JavaScript code segments may only be executed in certain situations as a result of conditional statements or branches. The related code is no longer needed if these requirements are infrequently or never met.
  • Testing or Debugging Code – JavaScript may be left unused if code snippets added for testing or debugging such as console logs or temporary functions are not removed before the application is deployed.
  • Legacy Code – Older JavaScript code that is no longer applicable or required for the application’s current version may be present in inherited projects or codebases.
  • Unused Variables and Functions – Over time, changes in requirements or code evolution may result in the accumulation of unused variables, functions, or classes within the codebase, which can lead to unused JavaScript.
  • Lazy Loading – Certain JavaScript modules may only be loaded when necessary as a result of lazy loading. Certain modules stay unused if they are never called upon by the user when interacting with the application.

How to detect Unused JavaScript Code?

The JavaScript code that is unused can be identified with the help of several tools.

These tools offer an extensive set of features and capabilities that enable find, remove, and optimize JavaScript code that isn’t needed in the projects, improving maintainability, performance, and efficiency.

Some of the commonly used tools are:

  1. Browser developer tools (e.g) Chrome DevTools
  2. PageSpeed Insights
  3. GTMetrix
  4. Lighthouse Audits
  5. Third party tools (e.g) Web Bundle Analyzer.

Methods for reducing Unused JavaScript Code

Reducing unused JavaScript is essential for improving website performance and enhance Technical SEO.

Here are few techniques to accomplish this:

Tree Shaking

A common technique used in modern JavaScript build tools such as webpack is tree shaking.

It removes the dead code from the JavaScript bundles during the build process.

Set up the build tool like webpack to enable tree shaking by setting the “optimization.usedExports” option to “True”.

Code Splitting

Splitting the JavaScript codebase into smaller sections or bundles, and loading them dynamically on demand is known as code splitting.

Identify and separate the modules or features that are not immediately needed for the initial page load into different bundles.

To load these bundles without delay when needed, use dynamic imports like ‘import()’ syntax.

This method improves SEO by enabling faster rendering of the page.

Lazy Loading

Delaying the loading of JavaScript code that isn’t necessary until it is needed is known as lazy loading.

The initial page load time can be greatly shortened by doing this.

For resources like images, scripts, and other elements that are not necessary for the initial rendering of the page, implement lazy loading.

This technique also improves the SEO performance metrics like Time to Interactive (TTI).

Conditional Loading

To load JavaScript resources in response to specific circumstances or user inputs, use conditional loading.

For example, instead of loading the JavaScript code for a specific feature upfront with the initial page load, only load it when the user accesses the feature.

Management of Dependencies

By regularly reviewing and managing the dependencies of the project, make sure only the libraries and modules that are necessary for the application will be included.

For the purpose of eliminating unnecessary dependencies from the project, use tools like npm audit or depcheck.

Linting and Static Evaluation

To find and eliminate unused variables, functions, and imports from the JavaScript codebase, use static analysis tools such as ESLint.

Configure ESLint rules to highlight unused code and enforce code quality standards on the entire project.

Server Side Rendering (SSR)

Take into account server-side rendering for the website, especially for content-rich pages or pages with significant SEO importance.

SSR generates HTML content on the server, reducing the need for client-side JavaScript and enhances search engine optimization by making sure that page content is easily indexed by search engine crawlers.

How to prevent Unused JavaScript Code: Best Practices

To maximize the performance of the application and to prevent unused JavaScript from accumulating in the codebase, consider implementing the following best practices:

  • To manage and find unused code more easily, organize the codebase into separate files or modules based on their functionalities.
  • Review the code frequently to find and eliminate any unnecessary imports, variables, and functions.
  • Include static analysis into your development process by using tools such as ESLint to flag unused variables, functions, and imports.
  • Make sure the libraries and packages that are required for the application are only included, by periodically reviewing and updating the dependencies for the project.
  • Make sure that tree shaking is enabled in the build tool and that any unnecessary exports are removed from the code.
  • Reduce the initial payload size of the application by dynamically loading modules only when they are needed.
  • Regularly monitor the application’s performance using tools like Google PageSpeed Insights, Lighthouse or web analytics platforms to address performance issues which include unused JavaScript.


In conclusion, eliminating unused JavaScript is not only for optimizing performance but also an essential practice to maintain a clean, efficient, and maintainable codebase.

By making use of a variety of strategies like code reviews, modular development, tree shaking, and performance monitoring unused JavaScript codes can be identified and eliminated.

These techniques not only optimizes the website’s speed and  responsiveness, but also improves development workflows and enhances overall code quality.

As the web technologies advances, prioritizing the elimination of unnecessary JavaScript is crucial for providing outstanding user experiences and guaranteeing the long-term sustainability and scalability of web projects.

By adopting these practices, it guarantees a more effective and user-friendly website and aligns with the overall objective of achieving higher search engine rankings and driving increased organic traffic.

Frequently Asked Questions

How to measure the impact of reduced Unused JavaScript Code on the website performance?

The impact of reduced unused JavaScript is measured by using performance monitoring tools like Google PageSpeed Insights, Lighthouse or web analytics platforms.

The success of the optimization efforts can be evaluated with these tools which offer insights into important performance metrics like page load times, time to interactive, and overall user experience.

Does Eliminating Unused JavaScript Code have a particular priority list?

In general, it is advisable to start by eliminating the biggest and most significant unused JavaScript first.

This could involve eliminating whole libraries or dependencies that aren’t being used to their full potential.

After addressing the most significant causes of unnecessary JavaScript code, then minor adjustments and refinements can be focused to further minimize unnecessary code.

What techniques are used to remove Unused JavaScript?

Some of the techniques for eliminating unused JavaScript include tree shaking, code splitting, dependency management, and dynamic imports.

By using these techniques, unnecessary code can be reduced and the size of the JavaScript bundles are optimized.

Picture of Ashkar Gomez

Ashkar Gomez

Ashkar Gomez is the Founder of 7 Eagles (a Growth Marketing & SEO Company). Ashkar started his career as a Sales Rep in 2013 and later shifted his career to SEO in 2014. He is one of the leading SEO experts in the industry with 8+ years of experience. He has worked on 200+ projects across 20+ industries in the United States, Canada, the United Kingdom, UAE, Australia, South Africa, and India. Besides SEO and Digital Marketing, he is passionate about Data Analytics, Personal Financial Planning, and Content Writing.

Table of Contents

Related Articles

Your Business
Starts Here

Let’s Have a Cup of Digital Tea

Request Your Free Quote

Book Your Free Marketing Consultation

Your Monthly ads spend