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Since MediaWiki 1.26, gadgets are now required to use ResourceLoader - see ResourceLoader/Migration guide (users) for more details.

ResourceLoader is the delivery system in MediaWiki for the optimized loading and managing of modules. Modules consist of JavaScript, CSS and interface messages. ResourceLoader was created in 2010 by Roan Kattouw, Trevor Parscal, and Timo Tijhof. The system was first released in 2011 as part of MediaWiki 1.17. It provides MediaWiki a high-performant front-end with strong caching while still allowing fast deployment of new code that all clients receive within minutes.

About ResourceLoader[edit]

Overview over the entire resource loading process of MediaWiki
→ See ResourceLoader/Features for a complete walk through of ResourceLoader

On Wikimedia wikis, every page view includes hundreds of kilobytes of JavaScript. In many cases, some or all of this code goes unused due to lack of browser support or because users do not make use of the features on the page. In these cases, bandwidth, and loading time spent on downloading, parsing and executing JavaScript code is wasted. This is especially true when users visit MediaWiki sites using older browsers like Internet Explorer 6, where almost all features are unsupported, and parsing and executing JavaScript is extremely slow.

ResourceLoader solves this problem by loading resources on-demand and only for browsers that can run them. Although there is much more to it, the overall flow for client-side performance can be summarized by these 3 points:

  • Minifying and concatenating
    → which reduces the code's size and parsing/download time
    Both JavaScript files, CSS files and interface messages are loaded in a single special formatted "ResourceLoader Implement" server response.
  • Batch loading
    → which reduces the number of requests made
    The server response for module loading supports loading multiple modules so that a single response contains multiple ResourceLoader Implements, which in itself contain the minified and concatenated result of multiple javascript/css files.
  • Data URI embedding
    → which further reduces the number of requests, response time and bandwidth
    Optionally images referenced in stylesheets can be embedded as data URIs. Together with the gzipping of the server response, those embedded images, together, function as a "super sprite".




These presentations detail the purpose and results of ResourceLoader.


These presentations go more in-depth towards developers already familiar with MediaWiki development.



  • Requirements – requirements gathered during the creation of ResourceLoader.
  • Version 1 Specification – the design document for the creation of ResourceLoader.
  • Version 2 Specification – the design document for the 2011/2012 extension of ResourceLoader to support cross-wiki module loading.



The current implementation of the MediaWiki mobile view as provided by Extension:MobileFrontend has many caveats. For tips to using ResourceLoader to the best of its ability, please see Writing a mobile friendly ResourceLoader module.

Documentation FeaturesResourceLoader/Features · VocabularyResourceLoader/Vocabulary · Migration guide (users)ResourceLoader/Migration guide (users) · Migration guide (developers)ResourceLoader/Migration guide for extension developers · Developing with ResourceLoaderResourceLoader/Developing with ResourceLoader · Core modulesResourceLoader/Modules · Mobile supportResourceLoader/Writing a MobileFrontend friendly ResourceLoader module
Project information Status updatesResourceLoader/status · Version 1 Design SpecificationResourceLoader/Version 1 Design Specification · Version 2 Design SpecificationResourceLoader/Version 2 Design Specification · RequirementsResourceLoader/Requirements
Other JavaScript DeprecationsResourceLoader/Legacy JavaScript