Unused JavaScript refers to JavaScript code that is loaded on a webpage but never executed or needed for functionality. This extra code increases page load times, consumes more bandwidth, and negatively impacts user experience and search engine rankings. Removing unused JavaScript improves site speed, enhances performance, and ensures better SEO outcomes.

What is Unused JavaScript?

Unused JavaScript consists of scripts that are included in a webpage’s code but are not actually required for rendering or functionality. This can happen due to:

  • Old or legacy scripts that were once needed but are no longer in use.
  • JavaScript files that load site-wide but are only needed on specific pages.
  • Third-party scripts that add unnecessary code.
  • Unused functions or dependencies within JavaScript files.

When a browser loads a webpage, it must download, parse, and execute all JavaScript files before rendering the page. The more unused JavaScript a page contains, the slower it loads, which negatively impacts performance and user experience.

Why is Unused JavaScript a Problem?

Unused JavaScript affects a website in multiple ways, primarily in terms of performance, user experience, and SEO.

  1. Slower Page Load Times

Browsers must process all JavaScript files before rendering a page. Large amounts of unnecessary JavaScript increase time to interactive (TTI) and largest contentful paint (LCP), both of which are critical metrics in Core Web Vitals.

  1. Higher Bandwidth Usage

Loading unused scripts increases data transfer, affecting users on slower connections or mobile devices with limited bandwidth.

  1. Increased CPU Load on Devices

Executing excessive JavaScript consumes CPU resources, which can slow down a user’s device and cause performance issues, particularly on mobile devices with lower processing power.

  1. Negative SEO Impact

Google prioritizes fast-loading websites. Pages with high amounts of unused JavaScript can suffer from lower rankings due to poor Core Web Vitals scores. A slow website leads to higher bounce rates, which can further impact rankings.

  1. Wasted Crawl Budget

Search engine crawlers may struggle with indexing JavaScript-heavy pages. Googlebot processes JavaScript separately, and excessive scripts may delay or prevent indexing.

How to Identify and Remove Unused JavaScript?

To optimize JavaScript usage, you first need to identify which scripts are unnecessary. As an all-in-one SEO tool that fully automates your website analysis and search engine optimization efforts, you can use Raiser Tools to identify the unused JavaScript codes in your website, and remove them for optimum performance.

To get a better understanding of the power of Raiser and how it can improve your website’s performance, you can check out this page.

Best Practices for Managing JavaScript Efficiently

Here are some of the best practices for managing JavaScript efficiently for your website performance and SEO score:

  • Regularly audit JavaScript usage.
  • Prioritize critical JavaScript and delay non-essential scripts.
  • Use content delivery networks (CDNs) to serve JavaScript files faster.
  • Implement lazy loading for JavaScript-heavy features that are not needed immediately.
  • Optimize CSS and HTML to reduce dependency on JavaScript where possible.

How Unused JavaScript Affects SEO

Google’s ranking algorithm considers page speed and user experience as major factors, making JavaScript optimization essential for SEO.

  • Slower pages rank lower – Google penalizes slow websites, especially those failing Core Web Vitals.
  • Poor mobile experience – Heavy JavaScript negatively impacts mobile users, leading to higher bounce rates.
  • Indexing issues – Googlebot delays JavaScript execution, which can delay content indexing and affect rankings.