When it comes to unused JavaScript, things are simple: the more unused code your page contains, the longer it takes to open the site. Since no one wants to face poor site performance and further consequences, it is important to know how to detect and remove unnecessary JavaScript files from webpages.
What Does “Unused JavaScript” Mean?
There are two types of render-blocking JavaScript:
- Non-critical JavaScript — it’s not used for the content at the top of the webpage but may be used elsewhere.
- Dead JavaScript — it’s not used anymore. There may be fragments from previous versions of the page that are no longer linked or were used temporarily.
What Triggers This Issue?
Heavy and unnecessary JS files are usually caused by third-party codes (social sharing buttons, for example), plugins, or page builders your website uses. Besides, it can happen if you forget to delete some lines of code used for testing or other temporary purposes.
How To Check the Issue
The detection of unnecessary CSS or JavaScript files is already half the battle. There are some tools that underline unused codes. You may check it with the Google Chrome DevTools network panel. This guide explains in stages how to detect unnecessary code using Chrome’s coverage tab.
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Why Is This Important?
Unused functions will slow down your website’s loading speed because the browser has more work to do, including downloading, parsing, compiling, and evaluating the useless script. It delays the rendering parameter and consumes more cellular data. This affects the website’s performance and will eventually cause a poor user experience.
How To Fix the Issue
Here are several hints on how to fix the problem and improve your website performance:
- If your website is running on WordPress, you can remove the unused JavaScript from its pages using special plugins. For example, you can use AssetCleanUp, which also allows you to disable unused JavaScript files.
- Another option is to detect unused JS with Chrome DevTools and delete unnecessary files. This video will show you how to use this tool to find unused JavaScript and CSS.
- You may use some web developer tools such as Lighthouse. Although, this one will report the unused code on a particular page. You should be careful before removing it, as the code might still be used on another page.
- Try minifying JS to get rid of unnecessary characters from the code. The closure compiler will help you with that.
- Delaying non-critical JS of the page will also help reduce the browser execution time. Another way is to defer non-essential scripts using a cache plugin.
The final solution depends on the cause of the problem: for instance, if unused JavaScript is caused by some plugins, you can replace them with lightweight counterparts. Alternatively, you may optimize third-party JS by enabling them only when an onclick occurs.
