Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/themes/seven/js/mobile.install.js

@@ -0,0 +1,33 @@
+(function () {
+
+  "use strict";
+
+  function findActiveStep(steps) {
+    for (var i = 0; i < steps.length; i++) {
+      if (steps[i].className === 'is-active') {
+        return i + 1;
+      }
+    }
+    // The final "Finished" step is never "active".
+    if (steps[steps.length - 1].className === 'done') {
+      return steps.length;
+    }
+    return 0;
+  }
+
+  function installStepsSetup() {
+    var steps = document.querySelectorAll('.task-list li');
+    if (steps.length) {
+      var header = document.querySelector('header[role="banner"]');
+      var stepIndicator = document.createElement('div');
+      stepIndicator.className = 'step-indicator';
+      stepIndicator.innerHTML = findActiveStep(steps) + '/' + steps.length;
+      header.appendChild(stepIndicator);
+    }
+  }
+
+  if (document.addEventListener) {
+    document.addEventListener('DOMContentLoaded', installStepsSetup);
+  }
+
+})();

core/themes/seven/js/nav-tabs.js

@@ -0,0 +1,55 @@
+/**
+ * @file
+ * Responsive navigation tabs.
+ *
+ * This also supports collapsible navigable is the 'is-collapsible' class is
+ * added to the main element, and a target element is included.
+ */
+(function ($, Drupal) {
+
+  "use strict";
+
+  function init(i, tab) {
+    var $tab = $(tab);
+    var $target = $tab.find('[data-drupal-nav-tabs-target]');
+    var isCollapsible = $tab.hasClass('is-collapsible');
+
+    function openMenu(e) {
+      $target.toggleClass('is-open');
+    }
+
+    function handleResize(e) {
+      $tab.addClass('is-horizontal');
+      var $tabs = $tab.find('.tabs');
+      var isHorizontal = $tabs.outerHeight() <= $tabs.find('.tabs__tab').outerHeight();
+      $tab.toggleClass('is-horizontal', isHorizontal);
+      if (isCollapsible) {
+        $tab.toggleClass('is-collapse-enabled', !isHorizontal);
+      }
+      if (isHorizontal) {
+        $target.removeClass('is-open');
+      }
+    }
+
+    $tab.addClass('position-container is-horizontal-enabled');
+
+    $tab.on('click.tabs', '[data-drupal-nav-tabs-trigger]', openMenu);
+    $(window).on('resize.tabs', Drupal.debounce(handleResize, 150)).trigger('resize.tabs');
+  }
+
+  /**
+   * Initialise the tabs JS.
+   */
+  Drupal.behaviors.navTabs = {
+    attach: function (context, settings) {
+      var $tabs = $(context).find('[data-drupal-nav-tabs]');
+      if ($tabs.length) {
+        var notSmartPhone = window.matchMedia('(min-width: 300px)');
+        if (notSmartPhone.matches) {
+          $tabs.once('nav-tabs').each(init);
+        }
+      }
+    }
+  };
+
+})(jQuery, Drupal);