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ResourceLoader/Developing with ResourceLoader

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This is a high-level walkthrough of the PHP interface for ResourceLoader for understanding how to create module bundles with ResourceLoader.

For more about ResourceLoader, how it works, and why it works the way it does, see ResourceLoader/Architecture.

IntroductionEdit

On every page view, the JavaScript runtime starts with a registry of which bundles exist in the system, the relationships between them, and a hash of their current version. MediaWiki can be instructed to load one or more of these on a given page. These instructions take the form of an addModules() or addModuleStyles() function call in PHP. Typically from a special page, parser function, or OutputPage hook.

A bundle should generally represent all code needed together in the same end-user scenario. For example, the user-interface of the WikiEditor extension is 1 module bundle, loaded from the edit page (possibly conditional based on content type and user preferences).

Note that bundle generation is allowed to vary by site, skin, and user language. As such, the bundle can also include site-specific configuration variables, additional scripts and styles specific to one or more skins or languages, and additional dependencies or script files based on the configuration of the wiki and/or other installed extensions.

There may be small portions of the interface that are only used later or in some cases, but the general default should be to still bundle them together. Splitting modules should be reserved as an optimisation and coincide with measuring of the perceived performance problem and quantified with end-user benefit.

If you find yourself needing more than three modules for a single extension or core feature aiming to be deployed on Wikimedia Foundation wikis, reach out to Wikimedia Performance Team who may be able to help find or design alternate approaches to solve the problem at hand.

RegisteringEdit

Each module bundle needs a symbolic name that is unique on a given site.

For MediaWiki core, modules are defined in the /resources/Resources.php file.

For extensions, modules are defined via the ResourceModules attribute in your /extension.json file.

Below is an example of a module definition for an extension (see also: Extension registration ).

"ResourceModules": {
    "ext.myExtension": {
        "scripts": [
            "modules/ext.myExtension.core.js",
            "modules/ext.myExtension.foobar.js"
        ],
        "styles": "modules/ext.myExtension.css",
        "messages": [
            "myextension-hello-world",
            "myextension-goodbye-world"
        ],
        "dependencies": [
            "oojs"
        ]
    }
}

NamingEdit

It is conventional for extension bundles to carry the "ext." prefix and use name of the extension in lowerCamelCase form as the main segment of the module name. Additional segments should be separated by dots.

DefinitionEdit

For more about the keys of the module definition (such as scripts, styles, messages, etc) see ResourceModules.

Loading modulesEdit

Server-sideEdit

see also Manual:OutputPage.php and ParserOutput

While building the page, add one or more modules to the page by calling the addModules method on the OutputPage or ParserOutput object and passing it one or more module names (such as "mediawiki.foo", or "ext.myExtension.quux")

$outputPage->addModules( 'example.fooBar' );

OutputPage adds the given module names to the load queue of the page. The client side loader requests all of the components for this module (scripts, styles, messages, dependencies, etc.) and executes them correctly. If your module contains styles that affect elements outputted by PHP as well as elements created dynamically, then you should split the module. One for styling/enhancing the output, and one for dynamic stuff. The first module should only have stylesheets and be loaded with addModuleStyles (see #CSS). The other module will simply be loaded asynchronously by the client, not blocking further parsing of the page.

$outputPage->addModules( [ 'mediawiki.foo', 'ext.myExtension' ] );

To get a reference to OutputPage object from an extension, use the BeforePageDisplay hook.

CSSEdit

If you have CSS that should be loaded before the page renders (and even when JavaScript is unavailable), queue it via OutputPage::addModuleStyles. This will make sure the module is loaded from a <link rel=stylesheet> tag.

For styles relating to anything involving JavaScript, the preferred method is to include them with OutputPage::addModules which loads modules as a complete package in a combined request (scripts, styles, messages) dynamically (from a lightweight client in JavaScript). This is because it is more efficient for this purpose (single request for all resources), supports dependency resolution, request batching, is highly cacheable (through access to the startup manifest with all version numbers it can dynamically generate permanently cacheable urls), and reduces cache fragmentation (modules previously loaded on other page views are loaded directly from Local Storage). It should not be used for CSS-only modules.

Since dependency changes can be deployed independently from caching the page, static loading with addModuleStyles cannot use dependencies. And since you can't dynamically access the latest version of the startup manifest from static HTML without JavaScript execution, it cannot have versions in the urls either and are therefore cached for a shorter time.

In practice you should only use OutputPage::addModuleStyles for stylesheets that are required for basic presentation of server-generated content (PHP output and the core Skin). Separate this CSS from modules with JavaScript and styling of dynamically-generated content.

JavaScriptEdit

JavaScript files are, like CSS files, also evaluated in the order they are defined in a scripts or packageFiles array.

In the following example, one would use the entry "packageFiles": [ "index.js", "Foo.js" ] when registering the module.

// Foo.js
var Foo = {
    sayHello: function ( $element ) {
        $element.append( '<p>Hello Module!</p>' );
    }
};
module.exports = Foo;

// index.js
var Foo = require( './Foo.js' );
$( function () {
    // This code must not be executed before the document is loaded. 
    Foo.sayHello( $( '#hello' ) );
});

The page loading this module would somewhere use $this->getOutput()->addHTML( '<div id="hello"></div>' ); to output the element.

Passing information from PHP to JavaScriptEdit

See Package modules for how to bundle additional data on the server-side with your module. These can be configuration variables, or results of rich callbacks that generate data form anywhere else that serialise to JSON, or even generated JavaScript code.

Alternatively, you might want to lazy-load the data from the API (e.g. using the mediawiki.api library).

If you need to export information specific to the current page output, e.g. from a parser function, consider using a data- attribute and selecting it from JavaScript. Or if you need more complex data, call call addJsConfigVars() on the OutputPage or ParserOutput object. In rare cases where you can't access an OutputPage or ParserOutput object, the MakeGlobalVariablesScript hook be used.

Client-side (dynamically)Edit

Gadgets should list their dependencies through the "dependencies" options in their definition.

For user scripts, dependencies cannot be declared ahead of time (unlike gadgets). Instead, for user scripts, wrap the code in a mw.loader.using block, and specify the required modules. For example:

mw.loader.using( ['mediawiki.util','mediawiki.Title'] ).then( function () {
    /* This callback is invoked as soon as the modules are available. */
} );

This will guarantee that the specified modules are loaded. Don't worry about multiple (separate) scripts both asking the loader for the same module. ResourceLoader internally ensures nothing is loaded multiple times.

Conditional lazy loadingEdit

If you have a script that only needs another module in a certain scenario of the user interface, you can create small separate module (known as an "init module"), and from there use JavaScript to dynamically load the rest of the module.

Example:

var $sortableTables = $content.find( 'table.sortable' );
if ( $sortableTables.length ) {
    mw.loader.using( 'jquery.tablesorter' ).then( function () {
        $sortableTables.tablesorter();
    } );
}

Parallel executionEdit

If you have multiple asynchronous tasks, it is best to run these tasks in parallel. Use jQuery.when to track multiple separate asynchronous tasks (known as a "Promise", or a "Deferred"). Below is an example of waiting for and AJAX request, and the loading of ResourceLoader modules, and the "document ready" status:

// Good: These three processes run in parallel
$.when(
  $.getJSON( 'https://api.example.org/foo' ),
  mw.loader.using( ['mediawiki.util', 'mediawiki.Title'] ),
  $.ready
).then( function ( fooData ) {
 // This runs when the ajax request is complete, the modules are loaded,
 // and the document is ready
 $( '#example' ).attr( 'href', mw.util.getUrl( fooData.page ) );
} );

// Bad: These are nested, one waiting before the other starts:
$( function () {
  mw.loader.using( ['mediawiki.util', 'mediawiki.Title'] ).then( function () {
    $.getJSON( 'https://api.example.org/foo' ).then( function ( fooData ) {
      $( '#example' ).attr( 'href', mw.util.getUrl( fooData.page ) );
    } );
  } );
} );

// Less bad: Preloading with load()
$( function () {
  mw.loader.load( ['mediawiki.util', 'mediawiki.Title'] );
  $.getJSON( 'https://api.example.org/foo' ).then( function ( fooData ) {
      mw.loader.using( ['mediawiki.util', 'mediawiki.Title'], function () {
        $( '#example' ).attr( 'href', mw.util.getUrl( fooData.page ) );
      } );
  } );
} );

CSSEdit

Your styling resources can be either CSS or, since MediaWiki 1.22, LESS files. When writing styles we advise you to follow our conventions.

Media queriesEdit

You can use media queries when you define your modules, to specify when a CSS/Less file applies:

{	"styles": {
		"always.css": { "media": "screen" },
		"print.css": { "media": "print" },
		"high-resolution.css": { "media": "screen and ( min-width: 982px )" }
	}
}

In the above example, the always.css stylesheet will always apply to all screens, the print.css stylesheet applies on print (and in the "Printable version" mode), and the high-resolution.css stylesheet applies when the viewport width is at least 982 pixels. The contents of the corresponding CSS/Less file will then be wrapped in the defined media query:

/* Output of print.css by ResourceLoader */
@media print {
	/* Contents of print.css */
}

/* Output of high-resolution.css by ResourceLoader */
@media screen and ( min-width: 982px ) {
	/* Contents of high-resolution.css */
}

AnnotationsEdit

The CSS preprocessors in ResourceLoader support several annotations that you can use to optimise your stylesheets.

@embedEdit

See also ResourceLoader/Architecture#Embedding

If an image is specified with the CSS url() function and is small enough (up to 24kB) the annotation @embed can be used in a CSS comment. This instructs ResourceLoader to embed the image in the CSS output as a data URI. For example:

.mw-feedback-spinner {
    display: inline-block;
    /* @embed */
    background: url(mediawiki.feedback.spinner.gif);
    ...
}

If you view a ResourceLoader request for this module, you can see that ResourceLoader transformed this image file into an embedded data URL, with the external URL only as a fallback. Reformatted for clarity, the ResourceLoader response includes:

.mw-feedback-spinner{display:inline-block;
 background:url(data:image/gif;base64,R0lGODlhEgA...==);
 background:url(https://www.mediawiki.org/w/resources/src/mediawiki/mediawiki.feedback.spinner.gif?f41ed)!ie;
...
}

Browsers that support data URIs in CSS use the embedded image instead of making another network request.

MediaWiki version: 1.22

In MediaWiki 1.22 and newer you can also use a LESS mixin to specify an image, and the mixin function outputs the @embed directive for you. For example, the .background-image() mixin (in mixins.less in core) in your LESS file:

.mw-foo-bar {
    .background-image('images/icon-foo-bar.png');
    padding: 4px  0 3px 40px;
}

See also ResourceLoaderImage, which generates raster images and multiple colored icons from a single source SVG file.

@noflipEdit

See also ResourceLoader/Architecture#Flipping

To disable the flipping functionality for one CSS declaration or on an entire ruleset, use the @noflip annotation:

For example:

/* @noflip */ 
.mw-portlet-item { 
    float: left; 
    line-height: 1.25; 
}

/* This one flips! */ 
.mw-portlet-item { 
    margin-top: 0.5em; 
    /* ... except this one: */ 
    /* @noflip */ 
    margin-left: 0.75em; 
    font-size: 0.75em; 
    white-space: nowrap; 
}

DebuggingEdit

Toggle debug modeEdit

ResourceLoader supports complex client-side web applications in production and development environments. As these different environments have different needs, ResourceLoader offers two distinct modes: production mode and debug mode (also known as "development") mode.

Debug mode is designed to make development as easy as possible, prioritizing the ease of identifying and resolving problems in the software over performance. Production mode makes the opposite prioritization, emphasizing performance over ease of development.

It is important to test your code in both debug and production modes. In day-to-day development, most developers will find it beneficial to use debug mode most of the time, only validating their code's functionality in production mode before committing changes.

You can enable debug mode for all page views, or for a single page request (by appending ?debug=true to the URL); see ResourceLoader/Architecture#Debug mode for details on toggling it.

Server-side exceptionsEdit

ResourceLoader catches any errors thrown during module packaging (such as an error in a module definition or a missing file) in load.php requests. It outputs this error information in a JavaScript comment at the top of its response to that request, for example:

/**
 * exception 'MWException' with message 'ResourceLoaderFileModule::readStyleFile: style file not found: 
 * Problematic modules: {"skin.blueprint.styles":"error"}
 */

You can inspect the request in the network panel in the developer tools for most browsers, or you can copy the load.php URL and load it in a new browser window. Note that the HTTP request with a failing module still returns status 200 OK, it does not return an error.

You can also output errors to a server-side log file by setting up a log file ($wgDebugLogGroups) in $wgDebugLogGroups['resourceloader']. They aren't added to the main debug log ($wgDebugLogFile) since logging is disabled by default for requests to load.php (bug 47960).

Client-side errorsEdit

Unreviewed

JavaScript returned by ResourceLoader is executed in the browser, and can have run-time errors. Most browsers do not display these to the user, so you should leave your browser's JavaScript console open during development to notice them.

You can use ResourceLoader's mw.loader.getState() function to check the state of a module, for example enter mw.loader.getState( 'skins.vector.js' ) in your browser's JavaScript console. If it returns:

null
The module is not known to ResourceLoader. Check for typos, and verify whether the module registered and defined correctly.
registered
ResourceLoader knows about the module, but hasn't (yet) loaded it on the current page. Check your logic for adding the module, either server-side or client-side. You can force it to load by entering mw.loader.load( 'my-module-name' ).
error
Something went wrong, either server-side or during client-side execution, with this module or one of its dependencies. Check the browser console and Network inspector for error relating to a load.php request. Alternatively, consider reloading the the page in debug mode.
ready
The module loaded on the current page without errors.

Breaking cacheEdit

When making frequent changes to code and checking them in a browser, the caching mechanisms designed to improve the performance of web-browsing can quickly become inconvenient. When developing on a system which is not making use of a reverse proxy, you only need to force your browser to bypass its cache while refreshing. This can be achieved by pressing CTRL+F5 in Internet Explorer, or holding the shift key while clicking the browser's refresh button in most other browsers.

If you are developing behind a reverse proxy, you can either change the values of $wgResourceLoaderMaxage or use ?debug=true to bypass cache.

See also