View source for Wikipedia:User scripts/Guide

{{Wikipedia programs}}

{{Shortcut|WP:US/G}}

{{About|writing user scripts for use on Wikipedia|text=For instructions on how to install user scripts, see [[Wikipedia:User scripts#How do you install user scripts?|How do you install user scripts?]]}}

== Prerequisites ==
{{Wikibooks|JavaScript}}
To write user scripts, you will have to learn at least some of the programming language that they are written in: [[JavaScript]].

Try these links:
* [https://developer.mozilla.org/docs/Web/JavaScript Mozilla Developer Network's JavaScript site]
* [http://www.w3schools.com/js/ W3schools Javascript tutorial]
* [[JavaScript syntax]]
* [[jQuery]]

Also, it would definitely help if you tried using [[Wikipedia:User scripts|one of our scripts]] and got it working. The rest of this tutorial assumes you know where the various things are (all explained at ''{{Section link|Wikipedia:User scripts#How do you install user scripts?}}'').

== Forking an existing script ==
Starting out, it may be easier to modify an existing script to do what you want, rather than create a new script from scratch. This is called "forking". To do this, copy the script to a subpage, ending in ".js",<ref group="n." name="contentmodel">The actual requirement is that the page have contentmodel "javascript". Making a page whose title ends in ".js" will automatically give it that content model and indicates to readers that the page contains JavaScript.</ref> of your user page. Then, [[WP:US#How do you install user scripts?|install the new page]] like a normal user script.

== Writing a script from scratch ==

Although you can write a script directly in your [[Special:EditPage/Special:MyPage/common.js|common.js]] page or ''skin''.js (such as vector.js) page, it is usually better to create a new subpage for it in the form ''YourUserName/title''.js, where ''title'' is the name of your script. That keeps your main js pages from getting cluttered and is helpful when you have multiple scripts installed. You will also want to [[WP:US#How do you install user scripts?|install the new user script]].

=== Hello world ===

To make a [[Hello world]] program, insert the following code into your ''User:YourUserName/common.js'' file:

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">importScript('User:YourUserName/hello-world.js');</syntaxhighlight>

Next, create the page ''User:YourUserName/hello-world.js'', and insert this code:

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">$('#bodyContent').prepend('<p>Hello world!</p>');</syntaxhighlight>

This will write "Hello world!" on every page, below the title, until you remove the code. User scripts are written in [[JavaScript]], and both of the above code snippets are in JavaScript. The second snippet uses [[JQuery]], a JavaScript library that specializes in manipulating [[HTML]]. <code>$</code> is a JQuery [[Function (computer programming)|function]] that lets us target the [[HTML]] element we want. <code>#bodyContent</code> is a string in [[CSS selector]] syntax, and means target the HTML element with property <code>id="bodyContent"</code> . <code>prepend</code> is a JQuery function that inserts HTML code as a child of the <code>#bodyContent</code> element. <code><nowiki><p>Hello world!</p></nowiki></code> is the HTML code to be inserted.

=== Your first script ===
We will be writing a user script by modifying your common.js. For the purpose of this tutorial, we will write a simple version of the [[Wikipedia:WikiProject User scripts/Scripts/Quick wikify|Quick wikify]] module, which adds the <code><nowiki>{{Wikify}}</nowiki></code> maintenance template to the top of an article when you click a link called "Wikify" in the "More" menu. To begin, change <code>MODULE_NAME</code> in the module template to "Qwikify". Your template should look like this: 

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
// Qwikify
$( document ).ready( function () {
    MODULE_CODE;
} );
</syntaxhighlight>

In <code>MODULE_CODE</code>, we want to add the "Wikify" tab, so we will use the [[#Adding elements|<code>addPortletLink()</code> function]] (requiring the <code>mediawiki.util</code> module). Replace <code>MODULE_CODE</code> with a call to this function. Then we will bind an event handler so that when this link is clicked, we will call another function named <code>doQwikify()</code> that will actually execute the code. The <code>name</code> is what is shown on the tab, so set that to <code>'Wikify'</code>. Most tabs have an ID of <code>ca-''name''</code>, so set the ID to <code>'ca-wikify'</code>. The title (also known as [[mouseover]] or [[rollover]] text) should be something like <code>'Mark for wikification'</code>.

Lastly, we use jQuery's [//api.jquery.com/click/ .click()] to listen for clicks on this link, and when that happens, execute a function. After we call <code>doQwikify()</code>, it says <code>event.preventDefault()</code>. Since we clicked on a link, we need to tell the browser to prevent its default behavior (going to the URL, <code>'#'</code>). We want the page to stay right where it is at, so to prevent the browser from following the link, we prevent that and do our own custom action.

Altogether, your new function should look like this:

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
// Make sure the utilities module is loaded (will only load if not already)
mw.loader.using( 'mediawiki.util', function () {
    // Wait for the page to be parsed
    $( document ).ready( function () {
        // See the "Portlets (menus and tabs)" subsection below
        var link = mw.util.addPortletLink( 'p-cactions', '#', 'Wikify', 'ca-wikify', 'Mark for wikification');
        $( link ).click( function ( event ) {
            event.preventDefault();
            doQwikify();
        } );
    } );
} );
</syntaxhighlight>

Now, we must write our actual <code>doQwikify()</code> function. It will edit the edit box, so we need to get the name of that and its form. Viewing the source of the page shows that the form is named <code>editform</code> and the textbox is named <code>wpTextbox1</code>, meaning that the actual text is <code>document.editform.wpTextbox1.value</code>. To add {{tl|wikify}} (and two new lines), we simply do:

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
document.editform.wpTextbox1.value = "{" + "{wikify}}\n\n" + document.editform.wpTextbox1.value;
</syntaxhighlight>

(We separate the two "{" brackets in the front of the wikify template so it doesn't get expanded when we write this code on the wiki.)

Finally, we want to submit the form for the user. Luckily, JavaScript has a built-in function just for this named <code>submit()</code>. To submit our editing form, use <code>document.editform.submit()</code>. Your code should now look something like this:

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
function doQwikify() {
    document.editform.wpTextbox1.value = "{" + "{wikify}}\n\n" + document.editform.wpTextbox1.value;
    document.editform.submit();
}
</syntaxhighlight>

And that's it! Combine it all together and it should look like this:

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
// Make sure the utilities module is loaded (will only load if not already)
mw.loader.using( 'mediawiki.util', function () {
    // Wait for the page to be parsed
    $( document ).ready( function () {
        // See the "Portlets (menus and tabs)" subsection below
        var link = mw.util.addPortletLink( 'p-cactions', '#', 'Wikify', 'ca-wikify', 'Mark for wikification');
        $( link ).click( function ( event ) {
            event.preventDefault();
            doQwikify();
        } );
    } );
} );

function doQwikify() {
    document.editform.wpTextbox1.value = "{" + "{wikify}}\n\n" + document.editform.wpTextbox1.value;
    document.editform.submit();
}
</syntaxhighlight>

Save this to your ''User:YourUserName/common.js'' page. Then go visit a page such as the [[Wikipedia:Sandbox|Sandbox]], go into the "More" menu, click "Wikify", and watch the user script add the maintenance tag for you.

== Built-in scripts ==
All Wikipedia pages include some built-in [[MediaWiki]] JavaScript code, with variables and functions that can be used in user scripts. Some of them were already mentioned (<code>$()</code>, <code>importScript()</code>, <code>mw.util</code>). This code is generally loaded as [[mw:ResourceLoader/Core modules|ResourceLoader modules]] (some of it preloaded, some loaded on demand) and ends up in properties of these globally available objects:
* <code>mw</code> (<code>mediaWiki</code>) for MediaWiki core,
* <code>$</code> (<code>jQuery</code>) for [[mw:jQuery|jQuery]],
* <code>OO</code> for [[mw:OOjs|OOjs]].

Some commonly accessed properties of <code>mw</code> include <code>mw.config</code>, <code>mw.user.options</code>, <code>mw.util</code>, <code>mw.Title</code>, <code>mw.loader</code>, and <code>mw.hook</code>. <code>OO.ui</code> is the namespace of [[mw:OOUI|OOUI]]. See [[mw:ResourceLoader/Core modules]] for more details.

== Development and testing ==
The following [[development environment]]s can be used to develop and test your script.

=== Basic ===
*Using the preview button: You can edit your script directly on your [[Special:MyPage/common.js|/common.js]] page, then click [Show preview] and the new code is executed right away on the preview page. 
*Saving it: If required elements are missing on the preview page (for example, your script does something on history pages), you will have to save the script in order to test it. However, it is not convenient and creates unnecessary entries in the page history.
*Execute it in your browser's JavaScript console: All modern browsers come with a JavaScript console and other development tools. You can type or paste and execute your code there; script errors and warnings will also be shown there. How to open the console depends on your browser:
**In Google Chrome and Edge – press {{press key|Ctrl|Shift|J}}
**In Firefox – press {{press key|F12}}
**In Safari – press {{press key|Ctrl|Alt|C}}
:You may need to click the Console tab if a different pane is currently open.

=== Loading it from a localhost web server ===

The best and most recommended way to load a JavaScript file during development is from your local web server (see below for an easy way to install a web server). Put this string in your [[Special:Mypage/common.js|/common.js]]:

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
mw.loader.load( 'https://localhost/wikipediatest.js' );
</syntaxhighlight>

In some environments, you need to write this as:<ref>https://developer.mozilla.org/en-US/docs/Web/Security/Mixed_content</ref>
<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
mw.loader.load( 'http://127.0.0.1/wikipediatest.js' );
</syntaxhighlight>

Then run any [[web server]] on your computer and create the <kbd>wikipediatest.js</kbd> file in the appropriate folder. The code inside this file will be executed as if it was inside your personal script.

You can edit your <kbd>wikipediatest.js</kbd> file with any text editor, perhaps with syntax highlighting and other convenient features, save the file and simply reload any Wikipedia page to see the results. (You do not need to wait, and if your web server is nice or you set it right, you do not even need to [[Wikipedia:Bypass your cache|bypass your browser cache]].)

Most modern code editors and IDEs allow you to set up a localhost server –&nbsp;eg. use [https://atom.io/packages/atom-live-server atom-live-server] in [[Atom (text editor)|Atom]], and [https://marketplace.visualstudio.com/items?itemName=ritwickdey.LiveServer Live Server] in [[VS Code]]. [[WebStorm]] and [[PhpStorm]] have the feature built in, without requiring an extension. You can also use a third party program such as [[Node.js]]'s <code>npx http-server</code> command ([https://www.youtube.com/watch?v=hnTiNvv5Eec video tutorial]), or [[XAMPP]]. 

If you have [[Python (language)|Python]] installed, you can run <code>python -m http.server</code> from command-line from the folder your script is in.

On Windows, you could also use for example [https://www.ritlabs.com/en/products/tinyweb/download.php TinyWeb], less than 100&nbsp;kbyte on disk and not requiring installation. Save and unzip <kbd>tinyweb.zip</kbd> for example into <kbd>c:\Program Files\Tinyweb</kbd>, create a shortcut to <kbd>tiny.exe</kbd>, and add an argument in shortcut properties — path to your folder with <kbd>wikipediatest.js</kbd> and any file <kbd>index.html</kbd> (required). Start TinyWeb with this shortcut; unload it with Task Manager.

Note that this method doesn't work in [[Opera (web browser)|Opera]] 9.50 (and later) due to added security restrictions, see [http://www.opera.com/docs/changelogs/windows/950/ Opera 9.50 for Windows changelog]: "Local servers can use remote resources, but not vice versa". In [[Google Chrome|Chrome]], it may be necessary to [http://stackoverflow.com/a/25075349/6357045 enable SSL], otherwise the script will refuse to load.

=== Browser-specific ===
Some browsers allow you to automatically execute your JavaScript code on specific web pages. This way you do not have to be logged in to Wikipedia. One example is [[Tampermonkey]]. However, making user scripts work with one of these extensions might require some modifications to the script code.

=== Running pieces of code ===
You can run pieces of code on already loaded pages via the JavaScript console. See the [https://developer.chrome.com/docs/devtools/console/javascript/ guide for doing this in Chrome]. It works similarly in most other browsers. In addition, [[Chromium]]-based browsers have a [https://developer.chrome.com/docs/devtools/javascript/snippets snippets] feature where short pieces of JavaScript code can be saved and debugged.

== Publishing ==

Once you have finished the user script code, you can save it as a page so that others can import it. By convention, scripts are in your userspace and have titles ending in ".js",<ref group="n." name="contentmodel" /> for example "User:YourUsernameHere/MyCoolScript.js". Others can then [[WP:US#How do you install user scripts?|install the new script]].

== Text editors and debugging ==

=== Text editors ===
You can use anything from a simple [[text editor]], to a more feature-packed [[code editor]] or [[Integrated development environment|IDE]]. Here are some recommended editors, by operating system.

* Windows
** [[VS Code]] (cross-platform)
** [[Notepad++]]
* Mac OS X
** [[Xcode]]
** [[JEdit]] (cross-platform)
** [[Komodo Edit]] (cross-platform)
** [[Aptana Studio]] (cross-platform)
** [[TextMate]] (not free)
** [[Coda (web development software)|Coda]] (not free)
** [[PhpStorm]] (not free, cross-platform, a free license for MediaWiki Developers is also available<ref>https://lists.wikimedia.org/pipermail/mediawiki-l/2010-June/034396.html</ref>)
* Linux
** [[Neovim]]/[[Emacs]]
** [[gedit]] (may come with Linux)
** [[Kate (text editor)|Kate]], for KDE-based desktops
** [[GNOME Text Editor]], for [[GNOME]]

=== JavaScript Debuggers ===

These are typically built into browsers, in their DevTools window. Debuggers allow you to step debug (go through your JavaScript code line-by-line, hover over variables to see their values, etc.)

* [[Firefox]] - use Tools → JavaScript Console showing all JavaScript and CSS errors.
* [[Google Chrome|Chrome]] and [[Microsoft Edge|Edge]] - use Tools → Developer Tools.
* [[Safari (web browser)|Safari]] - Safari → Preferences → Advanced and enable the "Show Develop menu in menu bar" option. Then use Develop → Show Web Inspector to open up the development tools.
* [[Opera browser|Opera]] - use Tools → Advanced → Error Console showing all JavaScript and CSS errors.

== Basic techniques ==

=== Running code on page load ===

The personal <code>user</code> module (built from /common.js, /common.css and optionally the skin-specific files for the current skin; see [[#Writing a script from scratch|above]]) and [[Wikipedia:Gadget|gadgets]] are loaded on all pages. Most scripts will want to manipulate elements on the page; to do so the page needs to be ready (it may not be the case at the time the modules are loaded). We can defer execution of code by using a special function.

==== <code>$(document).ready(...)</code> ====
One option is <code>[//api.jquery.com/ready/ .ready()]</code> from [[jQuery]].

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
// Define our main function
function myScript() {
  // ... code ...
};

// Schedule it to run after the HTML page is parsed
$( document ).ready( myScript );

// This shorthand is also valid
jQuery( myScript );
</syntaxhighlight>

Since the function is called only once, many users prefer to shorten this code with an [[anonymous function]]:
<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
$( document ).ready( function () {
  // ... code ...
} );

// Or
jQuery( function () {
  // ... code ...
} );
</syntaxhighlight>

'' '''Note:''' <code>$</code> and <code>jQuery</code> are the same object; choosing between them is purely a matter of opinion.''

Many scripts use this function simply to add some script interface, such as a link in a portlet. Then the main part of the code is executed after the user clicks on that link.

==== <code>mw.hook('wikipage.content').add(...)</code> ====
However, if your code works with the content part of the page (the <code>#mw-content-text</code> element), you should use the <code>[https://doc.wikimedia.org/mediawiki-core/master/js/Hooks.html#~event:'wikipage.content' 'wikipage.content']</code> [[Hooking|hook]] instead. This way your code will successfully reprocess the page when it is updated asynchronously and the hook is fired again. There are plenty of tools that do so, ranging from edit preview to watchlist autoupdate.

Be sure to only work with the descendants of the <code>$content</code> element that your handler function takes and not the whole page. Otherwise, you may end up running the same code for the same elements many times. Note that the <code>'wikipage.content'</code> hook may be fired ''really'' many times.

Be cautious about what comes in the <code>$content</code> argument of the handler function. You should not assume it is the <code>#mw-content-text</code> element. It can be a small portion of the page, e.g. when it is previewed.

Code that works with page content and avoids the aforementioned pitfalls may look like this:

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
mw.hook( 'wikipage.content' ).add( function ( $content ) {
	const $target = $content.find( '.targetClass' );
	if ( $target.length ) {
		// Do things with $target
	}

	// Only perform some operations when it is #mw-content-text in the argument
	if ( $content.is( '#mw-content-text' ) ) {
		const $note = $( '<div>' )
			.addClass( 'myScript-note' )
			.text( 'MyScript has successfully processed the content!' );
		$content.prepend( $note );
	}
} );
</syntaxhighlight>

If your code works with page content and adds event handlers to DOM elements, then, instead of hooking to <code>'wikipage.content'</code> and looking for elements to attach event listeners to when it is fired, you may attach one event listener to an element outside of the content area or the whole <code>document</code> but filter events by a selector (see [https://api.jquery.com/on/#on-events-selector-data-handler jQuery's documentation]). That is, instead of writing <syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%" inline>$content.find( '.targetClass' ).on( 'click', ... )</syntaxhighlight> you can write <syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%" inline>$( document ).on( 'click', '.targetClass', ... )</syntaxhighlight>.

=== Finding elements ===
Every [[HTML]] element is a node in a [[Document Object Model|DOM]] model allowing scripts to access the element, for example, on the following HTML page.

<syntaxhighlight lang="html" copy style="min-width:fit-content; max-width: 40%">
<form name="frmname" id="frmid">
	<textarea name="txtname" id="txtid"></textarea>
	<input id="neighbor" />
</form>
</syntaxhighlight>

We can find element <code>textarea</code>:
* Using its <code>id</code>: <syntaxhighlight lang="js" copy style="min-width:fit-content; max-width: 40%" inline>$( '#txtid' )</syntaxhighlight>
* In the array of all elements with the same <code>tag</code>: <syntaxhighlight lang="js" copy style="min-width:fit-content; max-width: 40%" inline>$( 'textarea' )</syntaxhighlight>
* Using an element next to it: <syntaxhighlight lang="js" copy style="min-width:fit-content; max-width: 40%" inline>$( '#neighbor' ).prev()</syntaxhighlight>
* As a child of its parent: <syntaxhighlight lang="js" copy style="min-width:fit-content; max-width: 40%" inline>$( '#frmid' ).children( 'form' )</syntaxhighlight>
* As a form element, using <code>name</code>: <syntaxhighlight lang="js" copy style="min-width:fit-content; max-width: 40%" inline>$( '#frmid [name="txtname"]' )</syntaxhighlight>

'' [http://jsfiddle.net/compwhizii/j2QRf/ This example on jsFiddle] ''

The [//api.jquery.com jQuery API reference] is an excellent source for documentation.
<!--To see all the elements on the page and their relations simply look at the page source code.-->

=== Checking the current page ===
Many scripts are supposed to work only on some pages. You can check:

* The page type<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
if ( mw.config.get( 'wgAction' ) === 'history' ) {  // Continue only on history pages.
</syntaxhighlight>
* [[:mw:Manual:Interface/JavaScript#mw.config|<kbd>wg</kbd> (Wikimedia global) variables]]; many of them have the same meaning as [[Help:Magic words|Magic words]]<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
if ( mw.config.get( 'wgCanonicalNamespace' ) === 'User_talk') {  // Continue only on User_talk pages.
</syntaxhighlight><syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
if ( mw.config.get( 'wgPageName' ) === 'Article_name' ) {  // Continue only for the article "Article name".
</syntaxhighlight>

* Presence of elements (only in second and third parts of the script)<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
function func_start() {
   if ( $( '#editForm' ).length == 0  ) return; //No edit form  ? exit
   // …
</syntaxhighlight>

=== Portlets (menus and tabs) ===

{{main|Help:Customizing toolbars}}{{shortcut|WP:PORTLET}}

Portlets are MediaWiki's name for groups of links located in the topbar and sidebar. Here is a diagram of portlet ID's.

[[File:MediaWiki portlet names.svg|500px|thumb|[[MediaWiki]] portlets as seen in [[Wikipedia:Skin|Vector legacy skin]].]]

==== List of portlets (portlet types)<span class="anchor" id="List of portlets"></span> ====

* Top
** <span style="color:green;">p-personal</span> - The links at the top right of the page. "personal" stands for "personal tools".
** <span style="color:red;">p-namespaces</span> - The tabs on the left that never collapse. Not recommended, not much space. The article and talk tabs are located here.
**<span style="color:red;">p-views</span> - The tabs in the middle that never collapse. Not recommended, not much space. The favorite page star tab is located here.
**<span style="color:green;">p-cactions</span> - The items in the "More" tab's dropdown menu. "cactions" stands for "content actions".
** <span style="color:red;">p-search</span> - Adding things here will mess up the appearance of the search box. Not recommended.
* Left
** <span style="color:red;">p-logo</span> - Adding things here will mess up the appearance of the logo. Not recommended.
** <span style="color:green;">p-navigation</span>
** <span style="color:green;">p-interaction</span> - Has the title "Contribute".
** <span style="color:green;">p-tb</span> - Has the title "Tools". TB stands for toolbox.
** <span style="color:red;">p-coll-print_export</span> - Has the title "Print/export". Not a good place to add things, since this should just be for printing and exporting.
**<span style="color:red;">p-wikibase-otherprojects</span> - Has the title "In other projects". Not a good place to add things, since this should just be for links to other projects such as Wikisource, Wikibooks, etc.
** <span style="color:red;">p-lang</span> - Has the title "Languages". Not a good place to add things, since this should just be for languages.

==== Portlet structure ====
<syntaxhighlight lang="html" copy style="min-width:fit-content; max-width: 40%">
<div id="p-myname" class="portlet">
 <h5>Header</h5>
 <div class="body">
  <ul>
  <li id="..."> <a ...>  //Links
  <li id="..."> <a ...>
  ...
</syntaxhighlight>

==== Adding elements ====
There is a special function in <code>mediawiki.util</code>, <code>[https://www.mediawiki.org/wiki/ResourceLoader/Core_modules#addPortletLink mw.util.addPortletLink()]</code> that simplifies the process of adding your own links to portlets. The advantage of using this function is that your code should work across all skins, and not break when these skins change their HTML. Its parameters, in order:

* <code>portletId</code> – ID of the target [[#Portlets (menus and tabs)|portlet]]
* <code>href</code> – link URL
** Set to <code>'#'</code> if you do not need to open a page and want to use a JavaScript listener instead.
* <code>text</code> – human-readable link text
* <code>id</code> (optional) – unique ID of the item
** Use a prefix such as {{abbr|ca-|Content Actions (p-cactions)}}, {{abbr|pt-|Personal Tools (p-personal)}}, {{abbr|n-|Navigation (p-navigation)}}, or {{abbr|t-|Tools/Toolbox (p-tb)}} – for consistency with other links in the group of chosen <code>portletId</code>.
* <code>tooltip</code> (optional) – helpful text appearing on mouse hover
* <code>accesskey</code> (optional) – [https://www.w3schools.com/tags/att_global_accesskey.asp keyboard shortcut key]
** Set to <code>null</code> if you do not need it.
** Use <code>$( '[accesskey=x]' )</code> in the console to see if 'x' is already used.
* <code>nextNode</code> (optional) – element that this will be added in front of

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
// Several examples of portlet links

// Adds a link to your js file to the toolbox. tb = toolbox
mw.util.addPortletLink ( 'p-tb', mw.util.getUrl( 'Special:MyPage/common.js' ), 'My JS', 'pt-myvector', 'Visit your js file');

// Add a link to the edit page for your Notes in your personal links
// Note: We assume that short/pretty URLs are in use with ?action, ideally you would check for that.
mw.util.addPortletLink ( 'p-personal', mw.util.getUrl( 'Special:MyPage/Notes' ) + '?action=edit', 'My notes', 'pt-mynotes', 'Edit your personal notes' );

// Adds a link to prefix index for the current page to the toolbox
mw.util.addPortletLink ( 'p-tb', mw.util.getUrl( 'Special:Prefixindex/' + mw.config.get( 'wgPageName' ) ), 'Prefixindex', 'tb-prefixindex');

// Adds a link to logs for your account
mw.util.addPortletLink ( 'p-personal', mw.util.getUrl( 'Special:Log/' + mw.config.get( 'wgUserName' ) ), 'My logs', 'pt-mylogs');
</syntaxhighlight>

Or you can use JQuery. Simply attach it in another place with <code>.append()</code>, <code>.prepend()</code>, <code>.before()</code>, or <code>.after()</code>. [https://www.w3schools.com/jquery/jquery_dom_add.asp][https://javascript.info/article/modifying-document/before-prepend-append-after.svg]. Warning: This is fragile. You may get it working on a couple skins, but a couple other skins may look broken.

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
// Add a clickable button on the edit article page, above the edit summary.
$('.editOptions').prepend('<button type="button" id="my-custom-button">Do Things</button>');

// Add a listener to your button, that does something when it is clicked.
$('#my-custom-button').click(function(e) {
	// do things
});
</syntaxhighlight>

=== Removing elements ===

To hide an element, you can use JQuery's [//api.jquery.com/hide/ <code>.hide()</code>] function.

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
// Example: remove special characters toolbar from edit page
$( '#editpage-specialchars' ).hide();

// Or modify the CSS directly
$( '#editpage-specialchars' ).css( 'display', 'none' );
</syntaxhighlight>

Or you can do it by placing code in [[Special:Mypage/common.css|common.css]]:

<syntaxhighlight lang="css">
#editpage-specialchars {
	display:none;
}
</syntaxhighlight>

=== Adding menus ===
You can add menus using <code>mw.util.addPortlet()</code> (see [[wmdoc:mediawiki-core/master/js/module-mediawiki.util.html#.addPortlet|documentation]]). The menu will not show up until you put a portletLink in it. If you add a menu adjacent to #p-cactions, it will be a dropdown menu in the Vector and Vector 2022 skins, with the correct dropdown HTML added for you.

<syntaxhighlight lang="js" copy style="min-width:fit-content; max-width: 40%">mw.util.addPortlet('p-twinkle', 'TW', '#p-cactions');
mw.util.addPortletLink('p-twinkle', '#', 'Tag');
mw.util.addPortletLink('p-twinkle', '#', 'CSD');</syntaxhighlight>

=== Editing ===

==== Textarea with article wikicode ====
The most important element on the edit page is a <kbd><textarea></kbd> with the article text inside. You can reference it with

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
var $textbox = $( '#wpTextbox1' );
</syntaxhighlight>

You can manipulate it using the [https://doc.wikimedia.org/mediawiki-core/master/js/jQueryPlugins.html#.textSelection jquery.textSelection] ResourceLoader module.
<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
var $textbox = $( '#wpTextbox1' );
$textbox.textSelection( 'setContents', 'This is bold!' );
$textbox.textSelection( 'setSelection', { start: 8, end: 12 } );
$textbox.textSelection( 'encapsulateSelection', { pre: '<b>', post: '</b>' } );
// Result: Textbox contains 'This is <b>bold</b>!', with cursor before the '!'
</syntaxhighlight>

Or you can grab <code><textbox></code>'s text, create a [[string (computer science)|string]], modify it, then write it back. Note; other editing tools might not recognise your changes or cause conflicts if you use this methodology instead of the textSelection api.

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
// Get value.
let value = $('#wpTextbox1').val();

// Your code goes here. Do things to value. RegEx, .replace(), concatenate, etc.

// Then write it back.
$('#wpTextbox1').val(value);
</syntaxhighlight>

==== Editing toolbar ====
WikiEditor is now the default toolbar when editing the source code of articles, but some users are still using the original toolbar. You can turn on and off WikiEditor by checking and unchecking the "Enable the editing toolbar" check box in [[Special:Preferences#mw-prefsection-editing|your preferences]].<ref group="n.">See [[mw:Extension:WikiEditor/Toolbar customization]] for information on how to customize WikiEditor.</ref><ref group="n.">See [[User:V111P/js/addToolbarButtons]] for a script that allows you to easily add buttons to whichever of the two toolbars the user is using.</ref>

==== Edittools ====
There is another edit panel under textarea. Usually it is generated from [[MediaWiki:Edittools]] by [[mw:Extension:CharInsert|Extension:CharInsert]] and consists of a lot of JavaScript links. In the English Wikipedia, this approach was replaced by [[MediaWiki:Gadget-charinsert.js]] and [[MediaWiki:Gadget-charinsert-core.js]].

=== Doing something after another user script ===
Sometimes you may want to add or remove something from the DOM, but another user script edits the same area of the DOM. It can be random which user script finishes first, creating a [[race condition]].

One way to coordinate this is use the [https://doc.wikimedia.org/mediawiki-core/master/js/Hooks.html mw.hook] interface. Perhaps the other script sends a <code>[[#mw.hook('wikipage.content').add(...)|wikipage.content]]</code> event when it is done, or can be modified to do so (or you can ask the maintainer).

Another way to avoid this is to use a [https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver MutationObserver].

=== User settings ===
If you want your users to be able to manually set configuration variables, one way to do this is to have them place <code>window.scriptNameSettingName = 'value here';</code> in their common.js file. Then within your user script, you can read this value with <code>if ( window.scriptNameSettingName == 'value here' )</code>.

Notice that "scriptName" is one of the pieces of the variable name. This is important to help make sure the variable is unique.

Do not use <code>let scriptNameSettingName = 'value here';</code> in the common.js file. If the user forgets the setting, you may get undeclared variable errors.

If you want your user script to write and save configuration settings as it is running, you may want to have it write to its own .js file in the user's userspace. See [[User:Novem Linguae/twinkleoptions.js|twinkleoptions.js]] or [[User:Novem Linguae/redwarnConfig.js|redwarnConfig.js]] for examples.

== Preventing bugs ==

=== <nowiki>&lt;nowiki&gt; tags</nowiki> ===
You may want to place the following code at the top and bottom of your user script, in a comment. This will help prevent bugs, such as <code><nowiki>~~~~</nowiki></code> turning into your hard-coded signature when you save the page.

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">//<nowiki>

Your code here.

//</nowiki></syntaxhighlight>

If you need to print &lt;nowiki&gt; or &lt;/nowiki&gt; tags within your user script, use a trick such as <code>const tag = '</' + 'nowiki>';</code> to keep from messing up the nowiki tag on line 1 and on the last line.

=== Function scope ===

Do not declare named functions in the global namespace. For example, this is bad:

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">function submitEdit() {/* do stuff */}

$(function(){/* main code here */});</syntaxhighlight>

What if another of your user scripts also declares a <code><nowiki>submitEdit()</nowiki></code> function? This can lead to [[race conditions]] and hard-to-trace bugs. Instead, use classes named after your script, or place all your functions inside of an [[immediately invoked function expression]] (IIFE) such as <code><nowiki>$(function {});</nowiki></code>. JavaScript allows [[Nested function|nested functions]].

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">$(function(){
    function submitEdit() {/* do stuff */}
    
    /* main code here */
});</syntaxhighlight>

== Ajax ==
[[Ajax (programming)|AJAX]] (''asynchronous JavaScript and XML'') is a popular name for a web programming technique that queries the server or fetches content without reloading the entire page. This is great for API requests. We do not have access to the SQL database in front end code, so the [[mw:Action_API|MediaWiki action API]] (or one of the [[mw:REST_API|other APIs]]) is the main way we retrieve data.

=== Basic examples ===
==== mediawiki.api ====
MediaWiki provides some modules with helper functions facilitating the use of its API. The main modules available are
* [https://doc.wikimedia.org/mediawiki-core/master/js/mw.Api.html mediawiki.api]
If your script makes use any method or code provided by these modules, remember to indicate the dependencies with [[mw:ResourceLoader/Default_modules#mediaWiki.loader|mw.loader.using]] or, in case of gadgets, on its definition at [[MediaWiki:Gadgets-definition]].

This API has several advantages especially when dealing with POST requests. It provides automatic token refresh and retry, handles various error situations and does parameter request building for several common use cases like rolling back a revision.

Be sure to follow the [[meta:User-Agent policy|user agent policy]] by setting a user agent header (see code there). See also [[mw:API:Etiquette]].

==== Get the wikitext of a page ====
===== Using module <code>mediawiki.api</code>=====
Note: make sure to add <code>mediawiki.api</code> to your dependencies!
<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
function doSomethingWithText( wikitext ) {
	/* .. */
	alert( 'The wikitext of the page is:\n\n' + wikitext );
}
function doSomethingInCaseOfError () {
	/* .. */
	console.log( 'err' );
}
(new mw.Api()).get( {
	prop: 'revisions',
	rvprop: 'content',
	rvlimit: 1,
	indexpageids: true,
	titles: 'Wikipedia:Sandbox'
} )
.then( function ( data ) {
	var q = data.query,
		id = q && q.pageids && q.pageids[0],
		pg = id && q.pages && q.pages[ id ],
		rv = pg && pg.revisions;
	if ( rv && rv[0] && rv[0]['*'] ) {
		doSomethingWithText( rv[0]['*'] );
	}
} )
.catch( doSomethingInCaseOfError );
</syntaxhighlight>

===== Using jQuery $.getJSON =====
<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
$.getJSON(
	mw.util.wikiScript('api'),
	{
		format: 'json',
		action: 'query',
		prop: 'revisions',
		rvprop: 'content',
		rvlimit: 1,
		titles: 'Wikipedia:Sandbox'
	}
)
	.then(function ( data ) {
		var page, wikitext;
		try {
			for ( page in data.query.pages ) {
				wikitext = data.query.pages[page].revisions[0]['*'];
				doSomethingWithText( wikitext );
			}
		} catch ( e ) {
			doSomethingInCaseOfError();
		}
	})
	.catch( doSomethingInCaseOfError );
</syntaxhighlight>

===== Using jQuery $.ajax =====
Fetching a page content can be done using jQuery <code>$.ajax</code>, which does an HTTP [[GET (HTTP)|GET]] request.<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
$.ajax({
	url: mw.util.getUrl( 'Wikipedia:Sandbox' )
})
.then(function( data ) {
	alert( 'The remote page contains:\n' + data );
})
.catch(function() {
	alert( 'The ajax request failed.' );
});
</syntaxhighlight>

==== Edit a page and other common actions ====
Scripts can perform common actions (like editing, protection, blocking, deletion, etc.) through the [{{SERVER}}/w/api.php API]. These actions require an edit token, valid for any action during the same session. (However, you should get a new token for different tasks in case this changes in the future.)

The code below shows how to edit a page, but it can easily be adapted to other actions by reading the [{{SERVER}}/w/api.php API documentation].
===== Using module <code>mediawiki.api</code>=====
Note: make sure to add <code>mediawiki.api</code> to your dependencies!
<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
// Edit page via the mw.Api module.
// postWithEditToken( {} ) may be used instead of postWithToken("csrf", {} )
// for actions such as editing that require a CSRF token.
// The line "text: info.text," will cause the call 
// to replace entire page content with supplied data.
// alternatively, one can append or prepend the data to the page, by using
// "appendtext: info.text," or "prependtext: info.text," instead.
// when using "appendtext", it is possible to append the text to a specific section,
// by setting the optional field "section".
function editPage( info ) {
	var api = new mw.Api();
	api.postWithToken("csrf", {
		action: 'edit',
		title: info.title,
		text: info.text, // will replace entire page content
		summary: info.summary
	} ).done(function( data ) {
		alert( 'Page edited!' );
	} ).fail( function(code, data) {
		console.log( api.getErrorMessage( data ).text());
	} );
}
editPage({
	title: 'User:' + mw.config.get( 'wgUserName' ) + '/Sandbox',
	text: 'Cool! It works! :-) ~~' + '~~',
	summary: 'Trying to edit my sandbox [[Project:User scripts/Guide|using API]]...'
});
</syntaxhighlight>

===== Using plain jQuery =====
<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
// Edit page (must be done through POST)
// the line "text: info.text," will cause the call 
// to replace entire page content with supplied data.
// alternatively, one can append or prepend the data to the page, by using
// "appendtext: info.text," or "prependtext: info.text," instead.
// when using "appendtext", it is possible to append the text to a specific section,
// by setting the optional field "section".
function editPage( info ) {
	$.ajax({
		url: mw.util.wikiScript( 'api' ),
		type: 'POST',
		dataType: 'json',
		data: {
			format: 'json',
			action: 'edit',
			title: info.title,
			text: info.text, // will replace entire page content
			summary: info.summary,
			token: mw.user.tokens.get( 'csrfToken' )
		}
	})
	.then (function( data ) {
		if ( data && data.edit && data.edit.result && data.edit.result == 'Success' ) {
			alert( 'Page edited!' );
		} else {
			alert( 'The edit query returned an error. =(' );
		}
	})
	.catch ( function() {
		alert( 'The ajax request failed.' );
	});
}
editPage({
	title: 'User:' + mw.config.get( 'wgUserName' ) + '/Sandbox',
	text: 'Cool! It works! :-) ~~' + '~~',
	summary: 'Trying to edit my sandbox [[Project:User scripts/Guide/Ajax|using AJAX]]...'
});
</syntaxhighlight>

====Load JavaScript from Wiki page====

Security warning: Do not load Wikipedia pages that do not end in .js into your script using this method, because anybody can edit those pages.

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">let title = "User:YourName/YourScript.js";
mw.loader.load( "https://en.wikipedia.org/w/index.php?title="+title+"&action=raw&ctype=text/javascript" );</syntaxhighlight>

====Load JSON from Wiki page====

JSON is useful when you want to import complex data into your script. For example, maybe you have a bot that publishes certain data to a Wiki page regularly, and you want your script to read that data.

Careful with <code>ctype</code>. Set it to <code>raw</code> for normal Wiki pages, and <code>application/json</code> for pages where a template editor or admin has set the [https://www.mediawiki.org/wiki/Help:ChangeContentModel Content Model] to JSON.

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">let jsonData;
let title = "User:YourName/YourData.json";
$.getJSON(mw.config.get('wgScriptPath')+'/index.php?action=raw&ctype=application/json&title='+title, function(data){
	jsonData = data;
});</syntaxhighlight>

== Working with CSS ==

Some user scripts also use some CSS code, or even are built with CSS only. Then you need to code and test CSS code. That can be done via [[Special:EditPage/Special:MyPage/common.css|editing your ''User:YourUserName/common.css'' page]].

=== Loading a localhost file ===
For local development, you can load a CSS file from your local web server (see the previous section for an easy-to-install web server). Put this line at the top of your [[Special:Mypage/common.css|/common.css]]:
<syntaxhighlight lang="css" style="min-width:fit-content; max-width: 40%">
@import "http://localhost/wikipediatest.css";
</syntaxhighlight>
'''Note!''' Such <code>@import</code> statements must come before any other declarations in your CSS, except comments.

An alternative way is to put this line in your [[Special:Mypage/common.js|/common.js]] instead:

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
mw.loader.load( 'http://localhost/wikipediatest.css', 'text/css' );
</syntaxhighlight>

=== Publishing a CSS file ===

Once you have finished the CSS code, you either need to paste it into your <kbd>/vector.css</kbd> if it is only for personal use. Or if it is for use by others then you should upload it to for instance [[Special:Mypage/yourscript.css|User:Yourname/yourscript.css]]. Then other users can import it by putting the following line in their <kbd>/common.js</kbd> file. Note, that is in their ".js", not their ".css".

<syntaxhighlight lang="javascript" copy style="min-width:fit-content; max-width: 40%">
importStylesheet( 'User:Yourname/yourscript.css' );
</syntaxhighlight>

If the CSS should be used together with a user script written in JavaScript then you can make it easy for the users. Simply put the line above in the JavaScript code for your user script, then the users only need to "install" your JavaScript.

For completeness, in case someone wonders, users can import your <kbd>User:Yourname/yourscript.css</kbd> from their <kbd>/common.css</kbd> too. This of course has the advantage that it works even if the user has JavaScript disabled. Although it takes this slightly complex line of code:
<syntaxhighlight lang="css">
@import "/w/index.php?title=User:Yourname/yourscript.css&action=raw&ctype=text/css";
</syntaxhighlight>

==See also==
* [[mw:Gadget kitchen]]
* [[Wikipedia:User scripts/Techniques]]
* [[mw:ResourceLoader/Migration guide (users)]]
* {{Section link|mw:ResourceLoader/Core modules#jquery}}

==Notes==
{{reflist|group=n.}}

== References ==
{{reflist}}

{{Wikipedia:User scripts/Navbox}}
{{Wikipedia technical help|collapsed}}

[[Category:Wikipedia scripts| User scripts/Guide]]
[[Category:Wikipedia how-to]]