Common.js

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/* Any JavaScript here will be loaded for all users on desktop */

/* Add subpages toolbox link on user pages */
$(function() {
	var title = mw.config.get('wgTitle');
	if (mw.config.get('wgCanonicalNamespace') === 'User' && !title.includes('/') && mw.config.get('skin') !== 'timeless') {
		var subpagesLink = '/Special:PrefixIndex/User:' + title + '/';
		mediaWiki.util.addPortletLink('p-tb', subpagesLink, 'User subpages', 't-subpages', 'Subpages of this page');
	}
});

/* HiddenAppearances gadget helper functions */
function toggleAppearancesPane(eid) {
	e = document.getElementById(eid);
	if (e) { e.className = (e.className == "hiddenlist") ? "visiblelist" : "hiddenlist"; }
}
function showAppearancesPane(eid) {
	e = document.getElementById(eid);
	if (e) { e.className = "visiblelist"; }
}
function hideAppearancesPane(eid) {
	e = document.getElementById(eid);
	if (e) { e.className = "hiddenlist"; }
}

MediaWiki:Common.js