Board Thread:Support Requests - Getting Technical/@comment-4146635-20140517234855/@comment-856287-20140520223011

As far as I know, you have to implement an unsupported hack to get any custom JS to load on a chat page for everyone: Help:Custom chat JavaScript and CSS. Once you've set that up, Fubuki風吹's code would go in MediaWiki:Chat.js.

…but maybe there's an easier way to do it I'm not aware of.