A simple mu-plugin that buffers the entire WP process, capturing the final output for DOM manipulation.

Original code by kfriend on Stack Overflow. Licensed as GPL because it is a WordPress derivative.

To install, simply download and copy output-buffering.php to your /wp-content/mu-plugins directory.

Requires PHP 5.3 or higher.

Use HtmlPageDom in conjunction for jQuery-like DOM manipulation in PHP.

This code will replace any instance of "foo" on the web page with "bar":

add_filter( 'final_output', function( $output ) {
    return str_replace( 'foo', 'bar', $output );
});

By default, output buffering is only enabled on the frontend of the site and is disabled for WP Admin and during AJAX requests.

You can modify this behavior and specify on which request/screen types that you want to enable it by adding the following constants to wp-config.php:

define( 'OB_ENABLE_ADMIN', true ); // Enables output buffering in WP Admin
define( 'OB_ENABLE_AJAX', true ); // Enables output buffering during AJAX calls

define( 'OB_REQUEST_TYPES', array( 'site', 'admin', 'ajax' ) ); // Case-sensitive

In the example above, output buffering is enable on the frontend ("site"), in WP Admin ("admin") and during AJAX requests ("ajax"). Add or remove from the array as desired. For example, to only load output buffering in WP Admin and not on the frontend or during AJAX calls:

define( 'OB_ENABLE_SCREENS', array( 'admin' ) );

Take care when changing this behavior! You may experience issues when enabling in WP Admin or during AJAX calls if your manipulation logic interferes with normal WordPress function.

Always test first before using in a production setting!

1.0.5

• Disable output buffering for WP-CLI

1.0.4

• Disabled for WP JSON (Gutenberg compatibility)

1.0.3

• Added wp-config.php constants to control where output buffering is enabled.