MediaWiki:Gadget-CollapseTemplatesUsed.js

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// Collapse "Templates used on this page" at the bottom of Edit pages by default
mw.loader.using('jquery.makeCollapsible').then(function () {
  mw.hook('wikipage.content').add(function ($content) {
    var $ul = $content.find('.templatesUsed > ul.mw-editfooter-list.mw-collapsible');
    if (!$ul.length) return;
    // If not initialized yet, mark collapsed before init
    if (!$ul.hasClass('mw-made-collapsible')) {
      $ul.addClass('mw-collapsed').makeCollapsible();
    } else {
      // Already initialized: use the object API
      var obj = $ul.data('mw-collapsible');
      if (obj && typeof obj.collapse === 'function') {
        obj.collapse(); // reliable way post-init
      } else {
        // Fallback for older skins/builds
        $ul.addClass('mw-collapsed');
      }
    }
    // Sync the header button state
    $content.find('.templatesUsed .mw-editfooter-toggler')
      .attr('aria-expanded', 'false');
  });
});