ResourceLoader/Migration guide (users)

Through time the core JavaScript functions and HTML output improves functionality, introduces new methods, deprecates or changes in other aspects. This document intends to highlight the most common problems that need to be fixed.


 * For an overview of the modules that are available in MediaWiki core, see ResourceLoader/Core modules.
 * Problems with gadgets? Check if it's listed below. If so, ask a sysop to update it on your wiki.

= MediaWiki 1.37 =

jQuery Migrate 3
jQuery was upgraded to version 3 in MediaWiki 1.29 (released in 2017). In jQuery 3.0, several deprecated features were removed by upstream. We temporarily added these back through the jQuery Migrate layer to allow for a gradual transition (T280944).

In the developer console, you may find warnings like the following:"JQMIGRATE: jQuery.fn.size is deprecated and removed; use the .length property."or:"Uncaught TypeError: $elem.size is not a function."To understand how to update such code, use the following manuals:


 * jQuery Migrate 3 warnings reference
 * jQuery 3.0 Upgrade Guide
 * jQuery 3.5 Upgrade Guide

The following three issues may be difficult to find and have some extra tips:


 * HTML tags must be properly nested: This means you have used an invalid shortcut like . In older jQuery versions, this invalid HTML was automatically corrected to DIV, followed by P. In jQuery 3 the browser standard behaviour is followed, which means this becomes a P inside a DIV like  . To preserve the old behaviour, explicitly open and close your HTML. Like.
 * Cross-domain AJAX request with JSON-P: If you may cross-domain requests with  or   to APIs that returns executable JSON-P scripts (instead of plain JSON), then you must add the   option. In previous versions, jQuery would guess between secure JSON and insecure JSON-P scripts.
 * Calling .load as event method: It is no longer possible to call  . Use   instead.

= MediaWiki 1.35 =

user.tokens module
The  module has been merged into the   module bundle. The old module name is now an alias and has been deprecated in MediaWiki 1.35. It will be removed in MediaWiki 1.36 sometime later in 2020. – T235457

To remain compatible, update dependency lists or loader statements from " " to " ".

mediawiki.notify
The  module has been merged into the MediaWiki base environment. This module was responsible for providing the  function, which in turn lazy-loads the larger   module. – T233676

To remain compatible, simply remove " " from any dependency lists or loader statements.

= MediaWiki 1.34 =

jquery.ui.*
jQuery UI has been deprecated for years, but remains available due to slow switching to alternatives. As a part of on-going efforts to reduce bandwidth cost, the 27 deprecated jQuery UI modules have been collapsed into a single, still-deprecated mega-module (Gerrit, T219604).

To remain compatible, update dependency lists and loader statements from " " to " ".

accessKeyLabel
The  plugin has been available through   since 2014 (MediaWiki 1.24).

Depending on it directly is no longer supported as of MediaWiki 1.34. Update dependency lists and loader statements from "jquery.accessKeyLabel" to "mediawiki.util" to remain compatible.

mediawiki.RegExp
The  module has been available through   since 2015 (MediaWiki 1.25). – T218339

Depending on it directly is no longer supported as of MediaWiki 1.34. Update dependency lists and loader statements from "mediawiki.RegExp" to "mediawiki.util" to remain compatible.

The  function has also been deprecated (although kept as alias, shipping with "mediawiki.util"). Replace usage with.

jquery.tabIndex
The  module existed to help compute a low or high tab index on focusable elements on a page. In most cases this code was redundant. Lines of code involving  or   are often best removed entirely. The module is deprecated in MediaWiki 1.34. If the effect of this code is still wanted, it can be achieved in a simpler way without this JavaScript plugin. For example, to set a low tabindex, use. Or, to set a high tabindex, use  instead, like so: If you do need the exact behaviour of the original   function, use the following:

mw.user.tokens
The  key of   was deprecated in 2016 (MediaWiki 1.26). It has been removed in 2019 (MediaWiki 1.34). – T233442

The  key should be used instead. For example, change  to.

Note: The  class has not changed. Code like  will continue to work and should not be changed.

= MediaWiki 1.32 =

Api modules
All submodules  have been merged into the main module , so you only have to require the main module, and requiring submodules emits deprecation warnings. These submodules were kept as deprecated aliases to "mediawiki.api", and removed in MediaWiki 1.33.

Method, which was deprecated since MediaWiki 1.23, has been removed. Use  instead.

wgEnableAPI
The  and   keys of mw.config are deprecated as of MediaWiki 1.32, and will be removed in MediaWiki 1.35 (change).

The value of these configuration keys is always. Any check for them in JavaScript code is redundant and can be safely removed.

= MediaWiki 1.31 =

Internet Explorer 10 browser
With this version, we have stopped JavaScript support for IE10. See Compatibility for details.

jquery.placeholder
Deprecated in MediaWiki 1.29 (change), removed in MediaWiki 1.31.

The shim for the native placeholder attribute became obsolete as all supported browsers for JavaScript support this natively. Simply remove the call to.

= MediaWiki 1.30 =

The functionality was originally provided by a module called  in MediaWiki 1.17 (r76320). This was renamed to  in MediaWiki 1.19 (r94227).

The module was deprecated in MediaWiki 1.26, and removed in MediaWiki 1.30.


 * , : These have native JavaScript methods available now.
 * : No replacement, rarely used. Simple enough to do in plain JavaScript as.
 * : Moved to mediawiki.RegExp; later moved to.
 * : No replacement, rarely used. Use duck-type checks like  instead.
 * : No replacement, rarely used.

= MediaWiki 1.29 =

Legacy removals
JavaScript functions and variables part of  that had been deprecated since MediaWiki 1.17 or 1.18 have been removed:

User-Agent variables:.

DOM manipulation:.

Utilities:.

How to migrate
Below is a table containing migration information for the wikibits functionality. Many of the replacements are part of the  module, which is not loaded by default. Please declare your dependency on this module if you refer to, as described in the development guide.

Background
Since early 2011, gadgets with styles (both "only styles" and "styles and scripts") had their styles loaded twice. T42284 and https://gerrit.wikimedia.org/r/308096 address this bug.

What's new
This bug was addressed by adding support in the Gadgets extension for the ResourceLoader "type" feature. This allows gadget developers to configure how the module should be loaded Gadgets with only styles, internally get  by default. Gadgets with only scripts default to.
 * type=styles: Load module styles via, and completely omits loading any JavaScript files. (Loads styles early, applies styles before skin and page are ready, also works when JavaScript is disabled.)
 * type=general: Load module scripts and/or styles via . (Applies styles after the skin and page are ready, right before JS execution, has better caching.)

Gadgets with both scripts and styles currently default to loading both ways (just before the bug was fixed). When this happens, a warning is shown in the console that asks the developer to provide the desired type. Once we've given gadget developers enough time to migrate, we can make  the default for gadgets that have both scripts and styles.

To load styles through the  system, while also loading JavaScript files, two separate gadget definitions need to be specified.

How to migrate
If you see this warning, that means your gadget contains both scripts and styles. Here are two ways to fix the warning: As you can see, in most cases the solution is "type=general." And in the future, this will become the default and we will not load styles twice. Right now, loading twice remains the default for compatibility with older gadgets covered by point 2 above. Changing these mixed gadgets to type=general now would cause some styles to load too late and cause a "flash of unstyled content".
 * 1) If the styles in your gadget are there to provide styling for things created by the gadget, add " " to your gadget definition ("MediaWiki:Gadgets-definition").
 * 2) Or – If the styles in your gadget are there to provide styling for things that are part of the skin or on the page, then these styles should not be together with the scripts in the same gadget. Convert the gadget to two separate gadgets. One gadget that is styles-only, and the other with the scripts. If the scripts gadget also has its own styles, then also set " " on the original gadget (per point 1). If you want to keep presenting the modules as one gadget on the Preferences page, use.

Gadget peers
For a long time, gadget authors have been interested in being able to provide a visual enhancement for all pages and also accompanying some scripting logic to apply related changes to interactive interfaces created by other modules. This requires the gadget to have both scripts and styles, but most of the styles are not required by the scripts – rather, the styles should apply directly to the page without waiting for JavaScript. So far this required either creating two gadgets (and requiring users to enable both), or creating a single gadget with the downside of the styles applying slightly after the page loads.

To accommodate the use case of a single gadget providing both page styles (which don't depend on JavaScript) and JavaScript code with its own styles, a new setting was introduced:. This is similar to, except that where dependencies load before the main module (not before the page itself), peers will allow one to reference a separate gadget module that will be loaded regardless of whether JavaScript is enabled.

For example: * example [ResourceLoader|dependencies=mediawiki.util|peers=example-pagestyles] | example.js | example.css * example-pagestyles [hidden] | example-pagestyles.css This will register a gadget named "Example" in the preferences which, if enabled, will load example-pagestyles before the page renders. And, once JavaScript is available, the example module will also be loaded with its own dependencies, styles and scripts.

Internet Explorer 9 and pre-ES5 browsers
With this version, we have stopped JavaScript support for IE9 and other browsers that do not support ES5. See Compatibility for details.

= MediaWiki 1.27 =

Legacy default: mediawiki.util
The option was removed. This option allowed third-party MediaWiki administrators to re-enable the unconditional preload of  by default for all users (for backwards compatibility). It was disabled by default since MediaWiki 1.26, and has been disabled on Wikimedia wikis since 2014. Extensions, skins, gadgets and scripts that use the  module must express a dependency on it.

bits.wikimedia.org
The internal Wikimedia domain "bits.wikimedia.org" was deprecated sometime mid-2015. The following common paths should be migrated to avoid breakage once the domain is decommissioned (T107430).
 * →  . Moved back to local domains, alongside   and others.
 * → : Moved to local domain, sharing a hostname-agonistic Varnish cache.
 * → : Specific versions can now be accessed through the regular script path. Wikimedia's multiversion entry point automatically serves the file from to the wikis' current MediaWiki version. (T99096)
 * → : Specific versions can now be accessed through the regular script path. Wikimedia's multiversion entry point automatically serves the file from to the wikis' current MediaWiki version. (T99096)

Internet Explorer 8
Following the deactivation of JavaScript in Internet Explorer 6 and 7 in MediaWiki 1.24, JavaScript has been deactivated in Internet Explorer 8. See Compatibility for details.

= MediaWiki 1.26 =

Legacy gadgets
Gadgets are now required to use ResourceLoader. For many Gadgets, migrating to ResourceLoader will be as easy as adding  to its definition on MediaWiki:Gadgets-definition. If after adding that, the gadget is not working properly, consult the rest of this page to look for functionality that may have been removed since the gadget was last maintained. If you run into any issues or find features that don't work without a clear way of making it work, please reach out to MediaWiki developers and fellow gadget authors on the |talk page, via IRC, or on the wikitech-l mailing list.

Global variables are not global
When ResourceLoader loads a gadget script, it is not executed in global context. This means that local variables you define in the script are actually local, and not assumed to be also global. They are local to the function your code is wrapped in. It's best to modularize your code to avoid using globals, see "Globals" in MediaWiki's JavaScript coding conventions. However, if you need to export a variable to the global scope, you can explicitly assign them as  properties. For example:

Code within your gadget can access foo and bar. Code outside the gadget (or code evaluated as separate programs, such as legacy onclick handlers), can only access Quux..

, ResourceLoader debug mode still executes scripts in global scope (T64605), so your code may seem to work fine in debug mode but be broken in regular mode.

Font mw-geshi
The font-size of was often too small by default due to a font-family CSS bug. This was fixed in MediaWiki 1.26 (see (T28204).

The,  ,   and related classes no longer exist. Related code such as the following can be safely removed:

Inline scripts
To inject JavaScript inline, use  to wrap the JavaScript code in an anonymous function that can access MediaWiki-related objects properly, and   to add the results to the page source for execution.

For example:

= MediaWiki 1.24 =

Legacy removals
The  JavaScript module, deprecated in MediaWiki 1.23, has been removed. See rMW8f2ebcbf6769.

Internet Explorer
Browser support for Internet Explorer 6 and 7 changed from Grade A to Grade C. This means JavaScript is no longer executed in these browser versions. See Compatibility for details.

= MediaWiki 1.20 =

mw.util.jsMessage
This method has been deprecated in favour of mw.notify.

The jsMessage message was designed to be a drop-in replacement fully compatible with the legacy wikibits  function (deprecated since 1.17, removed in 1.29). The 2012 notification system on the other hand was designed with developer usability and security in mind.

For most cases, the new method is just as easy to use as the old one, and requires only a the same single parameter that represents the message. For example, with plain text: And another example, with a DOM element, or a jQuery object: If you're currently using raw HTML with, the simplest way to migrate is to do what jsMessage used to do internally for you, which is to parse the HTML and place the node(s) in a jQuery object, as follows:

New diff styles
This version introduces a new diff view, greatly improved in clarity especially for whitespace and other small changes and colour-blind users. If your wiki has custom CSS for the diffs, they may be in conflict with the new style (as happened on [//pt.wikipedia.org/w/index.php?title=MediaWiki%3ACommon.css&diff=29858952&oldid=28922245&uselang=en ptwiki] and [//sr.wikipedia.org/w/index.php?diff=5578051&oldid=5533214&uselang=en srwiki]). You are recommended to remove the old code (or if still wanted by some users, update it to work with the new layout and create a gadget for it so that users can opt-in to it still).

= MediaWiki 1.19 =

wikitable style updates
As of MediaWiki 1.19 a few bugs have been fixed with the  class (see T32485 and T35434 for more info). If your wiki maintains a legacy synonym of this class (e.g. " ") you need to update its CSS to match the current style in core.

The current style as of 1.19 can be found [//github.com/wikimedia/mediawiki/blob/1.19.24/skins/common/shared.css here]. Copy those rules to your wiki and replace "wikitable" with the synonym ([//nl.wikipedia.org/w/index.php?title=MediaWiki:Common.css&diff=29814645&oldid=29702942 example for nl.wikipedia]).

If your wiki doesn't keep something like this, then no update is necessary and everything should take care of itself.

File page checkered background
The checkered background often applied to transparent file namespace pages is now part of the software. Local rules like the following should be removed (because they are redundant, and actually cause an additional unnecessary HTTP request for the image)

Trackbacks
Trackbacks were removed from MediaWiki core, so any styling targeting  can be removed.

= MediaWiki 1.18 =

Protocol-relative urls

 * This change only applies to Wikimedia Foundation wikis.

As of MediaWiki 1.18 there is native support for protocol-relative wiki installations. This means that a wiki could be accessible from both http://example.org/ and https://example.org./ To make it possible to a share a common cache for as much as possible, we make use of a technique called protocol-relative urls. Although browsers have supports this for ages, script writers generally aren't very familiar with it until fairly recently. Briefly explained, this means that  when on " https://example.org " will be automatically expanded by the browser to https://meta.wikimedia.org./ This is much like (for example)   or , which are are automatically expanded to " http://mediawiki.org/w/foobar.jpg ".

Depending on how the scripts were written this may require some changes to be made to your scripts. If you use the following method to detect whether the script is executed on a certain wiki, this change will break your script: because wgServer is now " ". For a few years there has been another config variable, called " ". You should use that instead to differentiate wikis, like: Alternatively, you can use  which is without the protocol or port:

"Enabled by default" (Gadgets extension)
As of the version of the Gadgets extension at the MW 1.18 branchpoint, there is a new feature that allows a gadget to be opt-out instead of opt-in based. By setting " " (or adding " " to an existing section) the gadget will be enabled by default for everybody, unless a user has specifically opted out by unticking the checkbox on Special:Preferences.

Note that this also loads it for all anonymous users. Gadgets that are only for logged-in users should be additionally restricted by, for example, requiring certain user rights.

See also Extension:Gadgets.

mw.util.wikiScript
The actual paths have not changed, but getting the path to the API and index.php has become a lot easier. This also makes the code more portable as it has no hardcoded wiki-specific paths.

This is how it used to go in many gadgets.

Instead use something like one of the following:

You may also want to use  to automatically escape and create things properly in the query string:

You can even use the  option of, that abstracts away the need to deal with the query string entirely:

= MediaWiki 1.17 =

jQuery

 * See also jQuery

As of 1.17 the jQuery library is loaded by default on all MediaWiki pages. Each MediaWiki release will keep it up to date with the latest version of jQuery. If you used to load jQuery from within your script, (e.g. from ajax.googleapis.com), make sure you remove that. If you load jQuery more than once on a page, it overwrites the earlier version. Other scripts break because they may not work with an older version of jQuery.

Also, by overwriting the jQuery object, any plugins that were bound to that object are also lost.

Global identifier " " has been deprecated. Use  or   instead.

Tabs (vector)
In 1.17 the HTML construction for the navigation tabs has changed from  to. The most common situation in which this causes problems is where scripts assume the presence of the span element when, for example, customizing the tab for "Main Page". Before 1.17 this usually meant that wikis had a different implementation for Monobook and one for Vector (or only one for each and the other was distorted).

Please use or refer to Snippets/Main Page tab for a script that will work in both Vector and Monobook for 1.17.

Adding portlet links
The legacy function  has been rewritten as. The syntax and argument order is fully backwards compatible. The differences
 * Support for all core skins now
 * Support for simple id-selector as 'nextNode' (see documentation for details).

Some wikis may have re-defined / overwritten the  function to support a few extra skins. This is no longer needed. The function definition should be removed and calls adjusted to.

The legacy version of  has been preserved as-is in case some edge cases would behave differently (for that reason the   does not redirect to mw.util.addPortlinkLink)

Toolbar
The legacy array  has been refactored into the   library. The global array still exists in wikibits to avoid fatal errors but is no longer used due to race conditions. Code may run too late when the toolbar already exists. Using  will work always, even if the toolbar has already been created.

See mw.toolbar Documentation.

Note that mw.toolbar, just like the old mwCustomEditButtons array, are associated with the classic toolbar. The current default wikitext editor is WikiEditor, which has its own API. See Extension:WikiEditor/Toolbar customization for more information.

Sajax
The legacy functions such as  have been deprecated. Instead,  from the   module, or. Migration guide:
 * mediawiki.api documentation
 * jQuery.ajax documentation

Client testing
Checking which browser, platform, layout engine etc. has should now be done with jQuery.client.
 * ,  etc. are deprecated
 * No need to  etc.

Sysop script
New in MediaWiki 1.17 is a user groups module that can automatically load scripts and styles from the MediaWiki namespace for a particular user group. For example, if the wiki has MediaWiki:Group-sysop.js, this script is automatically loaded for all users in that group.

This should obsolete customisations wikis may have with regards to loading MediaWiki:Sysop.js with importScript inside Common.js.

mw.loader
If you need certain scripts like jQuery UI's dialog or datepicker, instead of doing something like:

Instead use this:

Or if you need to delay initialization until document.ready:

Migrating user scripts
Contrary to, Wikibits.js functions such as   tend to be widespread among user script. Larger wikis may want to implement their own  function in MediaWiki:Common.js to make migration simpler. MediaWiki:Common.js is loaded as part of the "site" module which is guaranteed to load before the "user" module.

Dependencies
When a script depends on another module, such as  or , you will need to declare this as a "dependency". This is because modules are loaded on-demand and asynchronously (in consecutive order: all at the same time), so a script needs to make sure a module has been loaded before it can use its methods. On-site modules, like gadgets, have a registry to declare these dependencies. For user scripts, one has to wrap code with.

While this has been required since 2011, many scripts have continued to work without declaring their dependencies. Scripts may have worked before by accident as long as at least one user script (that used the same methods) did declare their dependencies and happened to load earlier.

With MediaWiki 1.19, page view performance has been optimised to use fewer modules by default. This makes it increasingly more important to declare the dependencies. Otherwise, your script may fail because any of the 1000+ modules you might refer to in your code would not be loaded yet. Loading everything all the time would be much too slow.

The only two base modules that are always present are  and.

In practice
Use  to declare any modules that you need before executing the contents of "function". You can pass multiple modules as an array of strings.

Global wg variables
As of MediaWiki 1.17, the global config variables are deprecated. Rationale to clear the global namespace, working towards a reality where most of the core libraries will be object oriented as part of the  object. Configuration is managed through an instance of  in. It is also supporting the behaviour of more script executing in their own local/private scope as opposed to the global scope.

Legacy globals will be kept for backwards compatibility, but people should start migrating so that they may removed in a future version of MediaWiki.

More info: ResourceLoader/Default modules

Ready, onload, hook
Check JavaScript deprecation overview for " ". Use  instead, or   for short.

Headings overflow hidden
for any of h1, h2, h3, h4, h5 and/or h6 can be safely removed from stylesheets as this is now part of the core.

Italic redirects
Links to redirects appear italicized on Special:AllPages, Special:PrefixIndex, Special:Watchlist/edit and in category listings

.allpagesredirect, .redirect-in-category, .watchlistredir { font-style: italic; }

wpSummary
Per T22276, 's   is now set in Vector as well (instead of just Monobook).

UsabilityInitiative no more
As of 1.17 the functionality developed by the UsabilityInitiative has been extracted to stand-alone extensions. Buttons like "#pt-optin-try" no longer exist. You can enable/disable these functions like other extensions via Special:Preferences.

Scripts and styles doing things like "HideUsabilityOptIn": should therefore be deleted entirely as the button no longer exists.

Preformatted JS/CSS pages
It's no longer useful to wrap these pages in  or    etc. In newer versions of MediaWiki, these pages are rendered as code automatically (including syntax highlighting when available). See also.

Table sorter
The old table sorter in  was removed in favour of.

Variables such as, and functions like   and   no longer exist.

= MediaWiki 1.16 and before =

importScript
As of 2008, the function  became part of MediaWiki. Wikis that had defined this function themselves were able to remove that. The new function would automatically be used. This was also true for,   and.

ImportScript has been deprecated since MediaWiki 1.29 and doesn't work on mobile sites like https://en.m.wikipedia.org/. Use mw.loader.load instead.

has been deprecated in favor of using jQuery directly. Use  instead of.

addPortletLink
As of 2008, the function  is part of MediaWiki. Many wikis and gadgets have created functions like,  ,   etc. these should be removed as they most likely don't support different skins (ie. only Monobook, not Vector or older skins). Be sure to check the syntax as there is no way of knowing the creator of those local functions used the same parameter order.
 * Note: The global function was deprecated in 2012 and moved to the mediawiki.util module as

appendCSS
As of 2008, the function  is part of MediaWiki. Wikis that have defined this function themselves may remove that. It will automatically use the new function.
 * Note: The global function was deprecated in 2012 and moved to the mediawiki.util module as

html lang
This bugfix is obsolete as MediaWiki does this correctly by default. (example)

wikitable
The  CSS class is part of MediaWiki. Wikis that previously defined this class in their  should remove it. Do check if the wiki has any customisations that should be retained (e.g. different background-color, or font-size).

plainlinks
The  CSS class is part of MediaWiki. Wikis that previously defined this class in their  should remove it.

Many wikis defined this functionality under a different name:. Once any usage is replaced with "plainlinks", it may also be removed. (Search with .)

mw-plusminus
The CSS classes,  , and   are now implemented by MediaWiki.

External URLs
Icons for protocols like [ HTTP], IRC, etc. and file types like [ PDF] are now supported by MediaWiki.

Tooltip and accesskeys
Scripts like  are ignored. It was deprecated in 2009. The function akeytt no longer exists. Tooltips and accesskeys are now supported from core. The most common values that wikis used with ta[] are the same that have now been integrated into the core (ie. "." for "my user page"). They can still be modified, if really needed, by sysops in MediaWiki-messages (no need for JavaScript workarounds anymore).

As of MediaWiki 1.19 the global dummy placeholder  was removed from. Code trying to add members to it will likely emit an exception.

= Best practices = The below are additional advices not related to a particular MediaWiki release, but rather general best practices.

Avoid document.write
Do not use this method, as it can cause a page to become visually blanked. Instead, use jQuery to modify the document (adding elements, changing things etc.). To load external resources, use the import/loader functions instead.

Example: replace with

Event binding
Binding input events to callback functions can be hard to do in cross-browser compatible way for all browsers that MediaWiki supports.

It is recommended that you use jQuery for event binding. See the JavaScript deprecation overview on "addHandler" for examples.

Encoding and escaping
When working with regular expressions, user input and/or urls must always be encoded or escaped.


 * Regexes:  (provided by   module).
 * HTML:  (provided by default).
 * URL:   for page titles,   for other values (provided by   module).

Prototyping
Do not extend native JavaScript constructors with non-standard methods (e.g.,  ,   etc.).

Such non-standard methods should be defined in your own namespace instead, for example, or using module.exports/require.

Polyfills
Before 2015, it was common for user scripts and gadgets to define fallback method for standard features of newer JavaScript engines. This is no longer needed in most cases, because the Base environment already ensures ES5 or later. This means ES5 methods such as  and   can be used directly.

Before MediaWiki 1.32, the es5-shim module was bundled with MediaWikii to automatically define polyfills if needed. It could be used like so:

Getting URL parameter values
Functions like getURLParamValue, getParamVal, getParamValue, etc. are very common across wikis. Some are better than others (i.e. what if a parameter appears twice? (it should return the last one), does it ignore anything after the #tag?). As of 1.17  is available everywhere and takes these factors into account. Perform a full-text all-namespace search for these function names. If they are widely used perhaps make a note about it in the local village pump. Any site-wide scripts should be updated to use the mw.util function. If there are any serious problems with the local implementation (like not escaping the value for regex), it may be wise to redirect the function:

Avoid use of !important
CSS stands for Cascading Style Sheets. Cascading means what comes later overwrites what came earlier. In most cases there is no need to use. See the following example: Text inside  will now be green.

Keep gadgets central
Use Meta.wikimedia.org or MediaWiki.org to store Gadgets' code, then import it into various local mediawiki.

Interface administrators: To update a gadget on your wiki:


 * Check on your wiki and find the gadget in question.
 * The part after the pipe is the scriptname (eg. "").
 * Go to (eg. MediaWiki:Gadget-UTCLiveClock.js)
 * Remove everything and replace with the code in they grey area below the scriptname in the list. For an example on how this is done, check out [ LiveClock on Simple Wikipedia].

Below is a list of gadgets that are :
 * centrally stored
 * compatible with 1.17
 * work in Monobook and Vector
 * can be loaded into any mediawiki, from WMF or external.

Gadgets

 * UTCLiveClock
 * contribsrange
 * modrollback
 * QPreview
 * ShortDiff
 * lastdiff Check Snippets/Last revision action
 * HotCat
 * WikiMiniAtlas
 * Navigation Popups (MediaWiki:Gadget-popups.js and MediaWiki:Gadget-popups.css respectively)

jQuery optimization

 * Optimization for jQuery
 * jQuery for Performance & Common mistakes
 * http://www.smashingmagazine.com/2008/09/16/jquery-examples-and-best-practices/

Use API instead of index.php
XML retrieved by invoking GET and POST methods on index.php is incompatible with HTML 5, which is the default as of 1.16 (and WMF sites since 17th of September, 2012). You should update code to use api.php, JSON format and jQuery.ajax immediately. Use the ResourceLoader modules that do this for you to simplify interactng with the API, including mediawiki.api.

A temporary fix for problems with DOM parsing of XML retrieved via AJAX: For example the method  on a XML object from Mozilla's DOMParser stopped to work as before. Replacing the  with   might work without many other changes to your code. Updating your script to the above mentioned methods is strongly recommended, however.

Conventions

 * Manual:Coding conventions/JavaScript – keep if statements with brackets, use proper indention (block B in block A is indented more, visualize the tree), etc.
 * Manual:Coding conventions/CSS – combine selectors, remove stuff now in core, etc.