Snippets/Load an additional JavaScript or stylesheet file on all pages

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Load an additional JavaScript or stylesheet file on all pages
Language(s):	PHP
Compatible with:	MediaWiki 1.23+

You can add snippets of JavaScript and CSS by editing special MediaWiki pages as described in Manual:Interface/JavaScript and Manual:Interface/Stylesheets. However, if you want to include additional scripts and stylesheet files without putting their contents on wiki pages, because you're using an external version control system or want to edit those files directly, this is a guide about how to include them.

This also solves the problem of CSS and Scripts not loading on special restricted pages like preferences or the login page.

Scripts hosted on the same wiki/server

Preparation

It's recommended to put your custom CSS and JavaScript files on a specific location, so you can track them during upgrades. In this example, those files will be inside a customizations folder, placed inside the MediaWiki installation folder.

We're going to use 3 files in this example:

skin.css: A stylesheet we want to load on all skins.
skin-vector.css: A stylesheet we want to load only on the Vector skin.
skin.js: A JavaScript file we want to load on all skins.

Code

This is an example code to add at the bottom of LocalSettings.php :

Javascript and associated CSS

To load a javascript and associated CSS for that Javascript use the following snippet. This adds a asynchronously load Javascript module and the CSS it requires. You might need an additional styles only module to avoid FOUC.

$wgResourceModules['zzz.customizations'] = array(
	'styles' => "skin.css", // Stylesheet to be loaded in all skins
	// Custom styles to apply only to Vector skin. Remove if you don't use it
	'skinStyles' => array(
		'vector' => 'skin-vector.css',
	),
	// End custom styles for vector
	'scripts' => "skin.js", // Script file to be loaded in all skins
	'localBasePath' => "$IP/customizations/",
	'remoteBasePath' => "$wgScriptPath/customizations/"
);

function efCustomBeforePageDisplay( &$out, &$skin ) {
	$out->addModules( array( 'zzz.customizations' ) );
}

$wgHooks['BeforePageDisplay'][] = 'efCustomBeforePageDisplay';

CSS only

To load CSS on the render critical path, use:

$wgResourceModules['yyy.customizations.styles'] = array(
	'styles' => "skin.css", // Stylesheet to be loaded in all skins
	// Custom styles to apply only to Vector skin. Remove if you don't use it
	'skinStyles' => array(
		'vector' => 'skin-vector.css',
	),
	'localBasePath' => "$IP/customizations/",
	'remoteBasePath' => "$wgScriptPath/customizations/"
);

function efCustomBeforePageDisplay( &$out, &$skin ) {
	$out->addModules( array( 'yyy.customizations.styles' ) );
}

$wgHooks['BeforePageDisplay'][] = 'efCustomBeforePageDisplay';

Scripts hosted externally

To add a script hosted externally, include it from the BeforePageDisplay hook:

$wgHooks['BeforePageDisplay'][] = function( OutputPage &$out, Skin &$skin ) {
	$out->addScriptFile( 'https://www.example.org/awesomescript.js' );
};

Note:

This bypasses the ResourceLoader dependency model
This adds additional domains, which is a performance penalty on the website user
You expose all your visitors to the security scope of the 3rd party website