How to really Fix "Reduce Unused JavaScript" in WordPress: A Deep Dive into Asset Management
Introduction: The Persistence of the PageSpeed PSI Warning
One of the most frustrating warnings in Google PageSpeed Insights (PSI) is "Reduce Unused JavaScript." Even after installing top-tier caching plugins and enabling "Delay JavaScript Execution," many developers find that this warning persists in the "Passed Audits" section only by a narrow margin—or not at all. To truly fix this, we need to look beyond simple minification and understand how WordPress handles assets.
1. Understanding the "Unused JavaScript" Metric
Google measures the percentage of bytes that are downloaded but not executed during the initial page load. While delaying scripts can improve the Total Blocking Time (TBT), it doesn't remove the unused code from the browser's memory entirely.
Standard optimization steps usually include:
- Minification & Compression: Reducing the file size of individual scripts.
- Defer/Async: Changing the priority of script execution.
- Delay Execution: Waiting for user interaction before loading specific scripts (e.g., scripts for analytics or chat widgets).
For advanced users, the standard recommendation for "fixing" this is to use wp_dequeue_script and wp_deregister_script in your functions.php. By wrapping these in conditional tags, you can theoretically stop scripts from loading on pages where they aren't needed:
PHP
PHP:
add_action( 'wp_print_scripts', 'my_dequeue_scripts', 100 );
function my_dequeue_scripts() {
if ( ! is_page( 'contact' ) ) {
wp_dequeue_script( 'contact-form-7' );
}
}3. Why Optimization Plugins Often Hit a Wall
Even with the best configuration, most optimization plugins operate at the "end" of the request. They take the mess that WordPress has already created and try to reorganize it. This leads to a fundamental realization about the platform's architecture:
"WordPress Loads Everything — Everywhere, All the Time."
When a plugin is active, it doesn't just add a script to the frontend; it often executes PHP logic, queries the database, and adds overhead to every single page load—regardless of whether its features are used on that specific URL. This is why "Optimization" often feels like painting a facade; you are trying to make a heavy system look fast without actually making it light.
4. The Shift to Performance by Prevention
The ultimate solution to "Unused JavaScript" isn't better organization—it's Prevention. If a script is unused, why was the plugin that generated it allowed to execute in the first place?
This is where we move from "Optimization" to the principle of "Don't use what you don't need."
5. Beyond the Facade: LiteCache Rush
To solve the "Everything, Everywhere" problem at its root, a different approach is required. Instead of managing assets at the frontend, we must prevent unnecessary code execution at the backend level.
Rush - Powered by LiteCache is designed for this exact purpose. It doesn't just hide unused JavaScript; it ensures that the code which produces the assets never executes if it isn't required for the specific request
- Speed comes from not doing things — not from doing them faster. By implementing Performance by Prevention, you eliminate the overhead before the browser even starts its audit. You aren't just fixing a PageSpeed score; you are finally letting your server breathe.