Table of contents

What is the WordPress polyfill script? Pros: Why removing polyfill might improve performance Cons: When you should not remove it How to check if your users need the polyfill How to safely remove the WordPress polyfill What breaks when polyfill is removed? How to replace the polyfill with a lighter alternative Getting started

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WordPress Guide → Development → Remove Polyfill

Should I remove polyfill from WordPress?

Is your WordPress site loading more JavaScript than it needs? If your visitors are mostly using modern browsers, removing polyfill could provide a slight performance benefit at no significant penalty. However, if compatibility with older browsers is a big concern, it’s better to keep the polyfill.

Let’s break down what polyfill does, when to remove it, and how to do it safely.

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What is the WordPress polyfill script?

Polyfills are JavaScript files that mimic modern browser features in older browsers. WordPress includes a built-in polyfill script (wp-polyfill) to ensure compatibility with outdated environments—especially browsers that don’t support features like Promise, Array.prototype.includes, or Object.assign.

This script is automatically included when a theme or plugin depends on core WordPress scripts that require modern JavaScript. While it helps with browser compatibility, it can also add unnecessary bulk if your visitors aren’t using legacy browsers.

Pros: Why removing polyfill might improve performance

The main reason to consider removing the polyfill script is performance. Here’s what you gain:

Reduced page size. Eliminating unused JavaScript can shave off kilobytes from each page load.
Faster load times. Less JavaScript means quicker rendering, especially on mobile networks.
Better performance scores. Tools like Google PageSpeed Insights and Lighthouse reward lean, modern codebases.

That said, the performance boost is usually minor—unless your site loads a lot of other scripts or serves primarily mobile users on limited bandwidth.

Cons: When you should not remove it

Keeping the polyfill is the safer choice in these situations:

Your audience includes users on older browsers, such as Internet Explorer 11 or early Android versions.
You use plugins or themes that rely on modern JavaScript features, which will break without fallback support.
You haven’t tested your site after removing it and want to avoid introducing bugs or broken layouts.

Removing polyfill when your site still depends on it can result in front-end errors or broken interactions—especially for forms, AJAX calls, and animations.

How to check if your users need the polyfill

Before removing anything, check what browsers your visitors are actually using. Here’s how to find out using Google Analytics 4:

Go to Reports > Tech > Tech Details.
In the primary dimension, choose Browser or Browser Version.
Look at the percentage of traffic from older browsers like Internet Explorer or legacy Safari versions.

If 99%+ of your users are on Chrome, Firefox, Edge, Safari, or mobile WebKit, you’re probably safe to remove the polyfill.

How to safely remove the WordPress polyfill

You can remove the polyfill manually by editing your theme’s functions.php file or creating a small plugin. Here’s how:

Open your theme’s functions.php file.
Add the following code:

function remove_wp_polyfill() {     wp_deregister_script( 'wp-polyfill' ); } add_action( 'wp_enqueue_scripts', 'remove_wp_polyfill', 100 );

Save and upload the changes.
Test your site in multiple browsers using DevTools and browser emulators.

If you prefer a plugin-based approach, you can use Asset CleanUp to selectively disable the polyfill script.

What breaks when polyfill is removed?

If your site or plugins rely on newer JavaScript features and you remove the polyfill, things might break. Common issues include:

JavaScript errors in older browsers, which prevent interactive elements from working.
Broken plugin UIs if the plugin uses ES6+ features without fallback support.
Admin panel glitches, especially if the editor or plugin settings depend on polyfilled features.

Always test your site in a staging environment before deploying changes to production.

How to replace the polyfill with a lighter alternative

Instead of removing the polyfill completely, you can take a more targeted approach:

Use a tool like Modernizr to detect missing features and load only what’s needed.
Load a custom, lightweight polyfill bundle from a CDN like Polyfill.io based on user-agent detection.
Use wp_register_script() to replace wp-polyfill with your own version.

Example code:

function replace_wp_polyfill() {    wp_deregister_script( 'wp-polyfill' );    wp_register_script( 'wp-polyfill', 'https://cdn.polyfill.io/v3/polyfill.min.js?features=default', [], null );    wp_enqueue_script( 'wp-polyfill' ); } add_action( 'wp_enqueue_scripts', 'replace_wp_polyfill', 100 );

This keeps your site functional on older browsers while minimizing the performance cost for everyone else.

Is it worth removing the polyfill?

Removing the WordPress polyfill can make your site leaner, especially if your visitors are using modern browsers. But if even a small slice of your audience still uses outdated software, it’s better to leave it in or swap it for a lighter alternative.

Only remove the polyfill if you’ve verified your user base, tested your site thoroughly, and are confident you don’t need it anymore.

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