Module Definitions

ResourceLoader modules are defined in extension.json under the ResourceModules key. Each module is a named object that declares its scripts, styles, dependencies, messages, and other properties. ResourceLoader reads these definitions and serves the module content via load.php.

A complete module definition

{
    "ResourceModules": {
        "ext.myExtension.feature": {
            "localBasePath": "",
            "remoteExtPath": "MyExtension",
            "scripts": [
                "resources/ext.myExtension.feature.js"
            ],
            "styles": [
                "resources/ext.myExtension.feature.less"
            ],
            "skinStyles": {
                "monobook": [
                    "resources/ext.myExtension.feature.monobook.less"
                ]
            },
            "dependencies": [
                "mediawiki.api",
                "mediawiki.util",
                "jquery"
            ],
            "messages": [
                "myextension-save-success",
                "myextension-save-error",
                "myextension-loading"
            ],
            "templates": {
                "item.html": "resources/templates/item.html"
            },
            "targets": [ "desktop", "mobile" ]
        }
    }
}

Module properties

scripts and styles

scripts lists JavaScript files to include. styles lists CSS or LESS files.

{
    "scripts": [
        "resources/myFeature.js",
        "resources/myHelper.js"
    ],
    "styles": [
        "resources/myFeature.less"
    ]
}

All paths are relative to localBasePath (which defaults to the extension root when using remoteExtPath).

packageFiles

packageFiles bundles JavaScript files into a CommonJS-style package where each file can use require() to import other files in the same module. This is the preferred approach for complex modules:

{
    "packageFiles": [
        "resources/index.js",
        "resources/api.js",
        "resources/ui.js"
    ]
}

The first file listed (or the file marked "main": true) is the entry point. Core uses this pattern extensively:

// From Resources.php — mediawiki.api module
'mediawiki.api' => [
    'localBasePath' => ...,
    'packageFiles' => [
        'index.js',
        'edit.js',
        'login.js',
        'messages.js',
        'options.js',
        'parse.js',
        'rest.js',
        'rollback.js',
        'upload.js',
        'user.js',
        'watch.js',
        'category.js',
    ],
    ...
]

packageFiles entries can also be objects with a callback for dynamic content:

{
    "packageFiles": [
        "index.js",
        {
            "name": "config.json",
            "callback": "MyExtension\\ResourceLoader\\MyModule::getConfig"
        }
    ]
}

dependencies

dependencies lists other module names that must be loaded before this module:

{
    "dependencies": [
        "mediawiki.api",
        "mediawiki.util",
        "oojs-ui-core"
    ]
}

ResourceLoader resolves transitive dependencies automatically. Circular dependencies cause a CircularDependencyError.

messages

messages lists i18n message keys that the module needs. The messages are loaded alongside the JavaScript and are accessible via mw.msg():

{
    "messages": [
        "myextension-save-success",
        "myextension-save-error"
    ]
}

In JavaScript:

// After the module is loaded, messages are available:
console.log( mw.msg( 'myextension-save-success' ) );
// "Your changes have been saved."

templates

templates maps template names to file paths. Templates are loaded as strings accessible via mw.templates:

{
    "templates": {
        "item.html": "resources/templates/item.html"
    }
}

In JavaScript:

var template = mw.template.get( 'ext.myExtension.feature', 'item.html' );
var $html = template.render( { name: 'Example' } );

skinStyles

skinStyles provides skin-specific CSS overrides. Use "default" to apply to all skins, or a skin name for targeted overrides:

{
    "skinStyles": {
        "default": [
            "resources/base.less"
        ],
        "monobook": [
            "resources/monobook.less"
        ],
        "vector-2022": [
            "resources/vector.less"
        ]
    }
}

Core uses this for Parsoid content styling:

'mediawiki.skinning.content.parsoid' => [
    'skinStyles' => [
        'default' => [
            'resources/src/mediawiki.skinning/content.parsoid.less',
            'resources/src/mediawiki.skinning/content.media-common.less',
            'resources/src/mediawiki.skinning/content.media-screen.less',
        ],
    ],
],

targets

targets controls which platforms a module is delivered to:

{
    "targets": [ "desktop", "mobile" ]
}

The default is ["desktop"]. To include a module on MobileFrontend-powered mobile pages, add "mobile".

Module types

Standard file modules

The default module type. Uses the FileModule class internally. Supports scripts, styles, packageFiles, dependencies, messages, templates, skinStyles, and targets.

Package modules

Modules using packageFiles are “package modules” — they bundle multiple JavaScript files into a single scope where files can require() each other. This avoids polluting the global scope.

// resources/index.js (entry point)
var api = require( './api.js' );
var ui  = require( './ui.js' );

module.exports = { api: api, ui: ui };

// resources/api.js
var myApi = { fetch: function () { /* ... */ } };
module.exports = myApi;

Startup module

The startup module (mediawiki.loader) is a special module managed by StartUpModule. It is the first module loaded on every page and bootstraps the entire ResourceLoader client. It registers all other module names, version hashes, and dependency graphs in a compact encoding. The startup module has reserved group IDs for certain module groups:

private array $groupIds = [
    // Reserved numbers MUST start at 0 and not skip any.
    // These are preset for forward compatibility so that they can be safely
    // referenced by mediawiki.js even when the order of registrations changes.
    self::GROUP_USER    => 0,
    self::GROUP_PRIVATE => 1,
];

Do not depend on mediawiki.loader or the startup module explicitly. ResourceLoader handles startup automatically.

Core module groups

jQuery modules

Module	Description
`jquery`	jQuery core library
`jquery.client`	Browser detection utilities
`jquery.confirmable`	Inline confirm/cancel prompts
`jquery.makeCollapsible`	Collapsible sections
`jquery.tablesorter`	Sortable table support
`jquery.chosen`	Select enhancement

mediawiki.* core modules

Module	Description
`mediawiki.base`	`mw` global, `mw.config`, `mw.message`
`mediawiki.api`	Action API client (`mw.Api`)
`mediawiki.util`	Utility functions (`mw.util`)
`mediawiki.notification`	Notification system (`mw.notification`)
`mediawiki.Title`	Title parsing and normalization
`mediawiki.Uri`	URL parsing
`mediawiki.storage`	localStorage wrapper
`mediawiki.cookie`	Cookie utilities
`mediawiki.jqueryMsg`	Advanced message parser
`mediawiki.router`	Client-side routing
`mediawiki.experiments`	A/B testing

Site and user modules

// Scripts managed by the local wiki (stored in the MediaWiki namespace)
'site'        => [ 'class' => SiteModule::class ],
'site.styles' => [ 'class' => SiteStylesModule::class ],

// Scripts managed by the current user (stored in their user space)
'user'        => [ 'class' => UserModule::class ],
'user.styles' => [ 'class' => UserStylesModule::class ],

// User preference values, exposed to JS
'user.options' => [ 'class' => UserOptionsModule::class ],

The site module loads MediaWiki:Common.js. The user module loads the active user’s User:Name/common.js. These modules belong to the site and user groups respectively and are loaded on every page.

Polyfills

Core includes a polyfill bundle for browsers that do not support modern web APIs:

'web2017-polyfills' => [
    'scripts' => [
        'resources/lib/intersection-observer/intersection-observer.js',
        'resources/lib/fetch-polyfill/fetch.umd.js',
        'resources/lib/url/URL.js',
        'resources/lib/url/URL-toJSON.js',
    ],
    'skipFunction' => 'resources/src/skip-web2017-polyfills.js',
    'dependencies'  => []
],

The skipFunction is evaluated client-side. If it returns true, the polyfill is skipped entirely, avoiding unnecessary download for modern browsers.

Extensions

Database

Parser & Content

ResourceLoader

Skins

Module Definitions

A complete module definition

Module properties

scripts and styles

packageFiles

dependencies

messages

templates

skinStyles

targets

Module types

Standard file modules

Package modules

Startup module

Core module groups

jQuery modules

mediawiki.* core modules

Site and user modules

Polyfills

Build docs developers (and LLMs) love

Extensions

Database

Parser & Content

ResourceLoader

Skins

​A complete module definition

​Module properties

​scripts and styles

​packageFiles

​dependencies

​messages

​templates

​skinStyles

​targets

​Module types

​Standard file modules

​Package modules

​Startup module

​Core module groups

​jQuery modules

​mediawiki.* core modules

​Site and user modules

​Polyfills

Build docs developers (and LLMs) love

A complete module definition

Module properties

scripts and styles

packageFiles

dependencies

messages

templates

skinStyles

targets

Module types

Standard file modules

Package modules

Startup module

Core module groups

jQuery modules

mediawiki.* core modules

Site and user modules

Polyfills