Performance BFCACHE

Improves browser Back/Forward Cache (BFCACHE) performance by blocking unload events for visitors.

Features

• Permissions-Policy Header: Adds Permissions-Policy: unload=() header to prevent unload event listeners from being registered.
• Visitor-Only Application: Only applies to visitors (non-logged-in users) to preserve admin functionality.
• BFCACHE Optimization: Improves page load performance when users navigate back/forward through browser history.

How It Works

The plugin sets a Permissions-Policy response header that blocks JavaScript from adding unload event listeners. This prevents pages from being excluded from the browser's Back/Forward Cache, resulting in:

• Instant Navigation: Pages load instantly when users click back/forward buttons
• Reduced Server Load: Cached pages don't require new server requests
• Better User Experience: Faster perceived performance for returning visitors

Installation

Using Composer

To install the plugin via Composer, follow these steps:

1. Add the Repository:

   • Open your project's composer.json file.

   • Add the following under the repositories section:

     "repositories": [
         {
             "type": "vcs",
             "url": "https://github.com/xwp/performance-bfcache"
         }
     ]

2. Require the Plugin:

   • Run the following command in your terminal:

     composer require xwp/performance-bfcache

3. Activate the Plugin:

   • Once installed, activate the plugin through the 'Plugins' menu in WordPress.

Usage

The plugin works automatically once activated. Example of the header output:

Permissions-Policy: unload=()

This header is only sent for:

• Homepage visits by non-logged-in users
• Blog posts and pages viewed by visitors
• Category, tag, and archive pages for anonymous users
• Search results for non-authenticated users

Admin Preservation

The plugin intelligently excludes the header when:

• Users are logged in and the admin bar is showing
• Viewing WordPress admin pages
• Making AJAX or API requests

This ensures that admin functionality that may depend on unload events continues to work normally.

Technical Details

The plugin hooks into WordPress's wp_headers action to add the Permissions-Policy header specifically for front-end page requests. It uses WordPress's is_admin_bar_showing() function to detect when users should receive the optimization.

Browser Compatibility

The Permissions-Policy header is supported by:

• Chrome/Chromium 88+
• Firefox 74+
• Safari 16.4+

Unsupported browsers will simply ignore the header without any negative effects.

Requirements

• WordPress: Version 5.0 or higher
• PHP: Version 7.4 or higher

Implementation Reference

This plugin follows the implementation guidelines from the Permissions Policy Unload Explainer.

License

This plugin is licensed under the GPLv3 or later.