Help:Advanced CSS and JS

Creating some custom code for your community or for your own account? This page goes a little further than our overview page to give you some helpful details.

Before you get started, though, you'll want to check out which pages can be customized. If you're planning to write some JavaScript for your community, you'll need to ask for it to be turned on by contacting Fandom Support. Finally, you'll want to familiarize yourself with the JavaScript review process.

CSS
The  HTML element on articles includes a unique identifier based on the name of the page. For example, on this help page, the class is

The general format is, where spaces, colons, and other special characters are replaced by underscores.

JavaScript
In MediaWiki:Common.js, use a switch to apply JavaScript to certain pages:

Applying CSS and JS to specific communities
In your personal CSS, you can add a class to the front of any other CSS selectors that will let you style the way your account looks at specific wikis.

This class is based on the database name of a community, not the URL — which are usually, but not always, the same. The format is:

or, if a non-English wiki:

For instance, if you wanted to make part of the background of Wookieepedia appear red to you, add this to your global.css file:



For JavaScript,  can be used to identify a specific community.

Load order
The general load order for both CSS and JS is:
 * 1) Fandom's core code
 * 2) local community code
 * 3) personal code

Within each level, the load order is Common first, then Wikia. This means that if you've said  in Common.css, but   in Wikia.css, the   will be green. And because personal CSS is last, whatever you put there always overrides the local wiki's choices.

It also critically means that if you're importing CSS or fonts — and your wiki has both Common.css and Wikia.css — those imports need to be at the very top of Common.css. If you want to simplify your wiki's CSS, you can graft the contents of Common.css onto Wikia.css. But you need to observe load order fundamentals when you do. Follow the nearby flowchart, and you'll be fine!

For JS, load order is especially important when considering how to best use MediaWiki:ImportJS. Because ImportJS loads last, you can put your customization of a Dev Wiki script in Common.js or Wikia.js, but have the import of the script itself in ImportJS. The full JS load order is:
 * 1) Common.js
 * 2) Wikia.js
 * 3) Imported scripts through Common.js
 * 4) Imported scripts through Wikia.js
 * 5) ImportJS

Finally, remember the obvious: pages load from top to bottom. That means that declarations made at the top of a page can be overridden by ones at the bottom.

!important in CSS
Due to CSS load orders, you may sometimes need to make use of the  property to ensure a CSS rule is applied. But  should be avoided when possible by use of specific (even overly specific) CSS selectors.

Caching issues
Every file you download from the internet gets cached. Normally that's great because it reduces traffic both for your own device and for Fandom's servers, but it can be a problem when it comes to testing design changes. It may take a while before your changes to take effect unless you bypass your cache.

If bypassing your cache doesn't work, you can try debugging your code by adding  at the end of the URL of any page. Debugging your code means that the code will almost 100% guarantee the load of the recently added script(s) and/or stylesheet(s).

Popular JavaScript snippets
To get an idea of some scripts others have written that you might find useful or would like to try, take a look at the list of JS Enhancements on the Fandom Developers Wiki.

Duplicate JavaScript
Many scripts can have problems if they are run multiple times on the same page. Make sure to write the code in such a fashion that a particular piece of code runs only once. Avoid pasting the same JS in multiple files as it will likely conflict and cause confusing errors for you and other visitors.

Temporarily disabling CSS/JS
Custom CSS and JS can be temporarily disabled using the following commands.

The command(s) should be added at the end of the URL ( example: ?usesitecss=0. [The following example disables site CSS]).

If more than one command is needed, instead of question mark, put an ampersand for the second, third and fourth commands (in case if there are) ( example: ?usesitecss=0&useuserjs=0. [The following example disables site CSS and personal JS]).

Here's a table of all the CSS/JS commands.

Note: The commands  and   do not currently work on UCP wikis. This is a known bug that is expected to be fixed sometime in the future. The commands  and   work partialy - they disable global personal code but not local personal code.

CSS and JS editor error checking
The CSS and JS editors have active error checking ("linting") and syntax highlighting:
 * As you type code, the page will let you know about any errors in the syntax that might have occurred.
 * Note that not every flagged issue has to be solved; CSS (and even JS) technology is ever evolving, and browsers do not all behave identically: some messages may not require action.

Further help and feedback
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