Website performance plays a crucial role in providing a seamless user experience, enhancing SEO, and improving conversion rates. One of the most significant factors influencing website speed is JavaScript, especially unused JavaScript. Google PageSpeed Insights and other performance testing tools often flag unused JavaScript as a common issue for slower load times.
In this article, we will explore what unused JavaScript is, why it affects Google PageSpeed, and provide actionable steps to reduce it, improving your site’s performance and SEO ranking.
What is Unused JavaScript?
Unused JavaScript refers to scripts or portions of JavaScript code that are loaded and executed on a webpage but aren’t utilized during the page’s visit. This can include functions, libraries, or features that aren’t being called or are only needed for specific conditions, such as on interactions that rarely occur.
For example, a script that loads an entire UI component library for a page that doesn’t use any of those components is a waste of resources. The browser still loads, parses, and executes that unused code, unnecessarily slowing down the page load time.
Why Unused JavaScript Impacts Google PageSpeed
Google PageSpeed Insights evaluates web pages based on their load performance, which directly impacts SEO. One of the factors considered is the First Contentful Paint (FCP), the time it takes for the first piece of content (like text or images) to appear on the screen. When unused JavaScript is blocking the main thread, it delays the rendering process, which increases the time it takes for users to see content.
Unnecessary JavaScript can also increase the overall size of the webpage, which affects the Time to Interactive (TTI). The larger the JavaScript bundle, the longer the browser takes to download, parse, and execute it, leading to a slower and less responsive site.
How to Reduce Unused JavaScript
Now that we understand the impact of unused JavaScript, let’s dive into actionable strategies to reduce it and enhance your Google PageSpeed score.
1. Audit Your JavaScript with Chrome DevTools
The first step in reducing unused JavaScript is to identify the culprits. Chrome DevTools provides a comprehensive way to spot and analyze unused JavaScript.
Here’s how to perform the audit:
- Open Chrome and go to the webpage you want to analyze.
- Right-click on the page and click Inspect.
- Go to the Coverage tab (found under the “More Tools” section).
- Reload the page while the Coverage tab is open.
- Chrome will show which lines of JavaScript were executed and which were unused.
Once you have this data, you can identify and remove or optimize the scripts that aren’t contributing to the page’s functionality.
2. Use Code Splitting
Code splitting is a technique that involves breaking down large JavaScript files into smaller chunks that can be loaded only when needed. This is particularly useful for single-page applications (SPAs) or websites with a lot of dynamic content.
For instance, if a user only needs to interact with a particular part of the site, you can load the necessary JavaScript only for that section, rather than loading the entire script upfront.
Tools like Webpack and Parcel offer code splitting features that can automatically separate and load JavaScript bundles only when required.
3. Lazy Load Non-Essential JavaScript
Lazy loading is a technique where non-essential JavaScript files or scripts are loaded only when they are needed, typically when a user interacts with a specific feature on your website (e.g., clicking a button or scrolling to a certain section).
For example, if your page includes a script for a carousel, you can lazy load it only when the user scrolls to that part of the page. This approach ensures that the browser doesn’t waste time loading unnecessary JavaScript upfront.
You can implement lazy loading with IntersectionObserver API or by using libraries like Lozad.js.
4. Remove Unnecessary JavaScript Libraries and Dependencies
Many websites include third-party libraries or frameworks (e.g., jQuery, Lodash) even though they may not be fully utilized across the entire site. Review the libraries you’re using and remove any that are redundant or not essential to the page’s functionality.
If you only use a small portion of a large library, consider using a tree-shaking tool that removes unused code during the build process. This is especially useful when working with modern JavaScript frameworks like React, Vue.js, or Angular.
5. Defer or Async Non-Critical Scripts
For non-essential JavaScript, you can use the defer or async attributes to modify how they are loaded.
defer: This attribute delays the execution of a script until the HTML document has been fully parsed. It ensures that scripts don’t block the rendering of content.async: This attribute allows the script to load asynchronously without blocking the page’s content rendering. However,asyncshould be used carefully as it may cause issues with script dependencies.
Both attributes help improve load time by making sure that scripts don’t block the initial page rendering.
6. Minify and Compress JavaScript
Although this step doesn’t directly reduce unused JavaScript, it can significantly improve load times by reducing the size of the JavaScript files. Minification removes unnecessary characters, like white spaces and comments, while compression (e.g., GZIP or Brotli) reduces the file size.
You can use tools like Terser or UglifyJS for minification, and ensure server-side compression for better file delivery.
7. Implement Server-Side Rendering (SSR)
Server-side rendering can reduce the reliance on JavaScript execution on the client side by rendering the HTML markup on the server before sending it to the browser. This is beneficial for performance because the browser doesn’t have to wait for JavaScript to load and render the page.
Frameworks like Next.js (for React) and Nuxt.js (for Vue.js) support SSR out of the box and offer better performance for dynamic content.
Conclusion
Reducing unused JavaScript is an essential part of improving your website’s performance and Google PageSpeed score. By auditing your code, using modern optimization techniques like code splitting, lazy loading, and removing unnecessary libraries, you can significantly enhance load times and provide a better user experience.
As Google continues to prioritise fast-loading websites in search rankings, taking the time to reduce unused JavaScript will not only improve your website’s speed but also boost its SEO, helping you attract more visitors and retain them for longer.