Navs

Documentation and examples for how to use Bootstrap’s included navigation components.

Base nav

Navigation available in Bootstrap share general markup and styles, from the base .nav class to the active and disabled states. Swap modifier classes to switch between each style.

The base .nav component is built with flexbox and provide a strong foundation for building all types of navigation components. It includes some style overrides (for working with lists), some link padding for larger hit areas, and basic disabled styling.

The base .nav component does not include any .active state. The following examples include the class, mainly to demonstrate that this particular class does not trigger any special styling.

Navs - 图1

  1. <ul class="nav">
  2.   <li class="nav-item">
  3.     <a class="nav-link active" href="#">Active</a>
  4.   </li>
  5.   <li class="nav-item">
  6.     <a class="nav-link" href="#">Link</a>
  7.   </li>
  8.   <li class="nav-item">
  9.     <a class="nav-link" href="#">Link</a>
  10.   </li>
  11.   <li class="nav-item">
  12.     <a class="nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Disabled</a>
  13.   </li>
  14. </ul>

Classes are used throughout, so your markup can be super flexible. Use <ul>s like above, <ol> if the order of your items is important, or roll your own with a <nav> element. Because the .nav uses display: flex, the nav links behave the same as nav items would, but without the extra markup.

Navs - 图2

  1. <nav class="nav">
  2.   <a class="nav-link active" href="#">Active</a>
  3.   <a class="nav-link" href="#">Link</a>
  4.   <a class="nav-link" href="#">Link</a>
  5.   <a class="nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Disabled</a>
  6. </nav>

Available styles

Change the style of .navs component with modifiers and utilities. Mix and match as needed, or build your own.

Horizontal alignment

Change the horizontal alignment of your nav with flexbox utilities. By default, navs are left-aligned, but you can easily change them to center or right aligned.

Centered with .justify-content-center:

Navs - 图3

  1. <ul class="nav justify-content-center">
  2.   <li class="nav-item">
  3.     <a class="nav-link active" href="#">Active</a>
  4.   </li>
  5.   <li class="nav-item">
  6.     <a class="nav-link" href="#">Link</a>
  7.   </li>
  8.   <li class="nav-item">
  9.     <a class="nav-link" href="#">Link</a>
  10.   </li>
  11.   <li class="nav-item">
  12.     <a class="nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Disabled</a>
  13.   </li>
  14. </ul>

Right-aligned with .justify-content-end:

Navs - 图4

  1. <ul class="nav justify-content-end">
  2.   <li class="nav-item">
  3.     <a class="nav-link active" href="#">Active</a>
  4.   </li>
  5.   <li class="nav-item">
  6.     <a class="nav-link" href="#">Link</a>
  7.   </li>
  8.   <li class="nav-item">
  9.     <a class="nav-link" href="#">Link</a>
  10.   </li>
  11.   <li class="nav-item">
  12.     <a class="nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Disabled</a>
  13.   </li>
  14. </ul>

Vertical

Stack your navigation by changing the flex item direction with the .flex-column utility. Need to stack them on some viewports but not others? Use the responsive versions (e.g., .flex-sm-column).

Navs - 图5

  1. <ul class="nav flex-column">
  2.   <li class="nav-item">
  3.     <a class="nav-link active" href="#">Active</a>
  4.   </li>
  5.   <li class="nav-item">
  6.     <a class="nav-link" href="#">Link</a>
  7.   </li>
  8.   <li class="nav-item">
  9.     <a class="nav-link" href="#">Link</a>
  10.   </li>
  11.   <li class="nav-item">
  12.     <a class="nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Disabled</a>
  13.   </li>
  14. </ul>

As always, vertical navigation is possible without <ul>s, too.

Navs - 图6

  1. <nav class="nav flex-column">
  2.   <a class="nav-link active" href="#">Active</a>
  3.   <a class="nav-link" href="#">Link</a>
  4.   <a class="nav-link" href="#">Link</a>
  5.   <a class="nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Disabled</a>
  6. </nav>

Tabs

Takes the basic nav from above and adds the .nav-tabs class to generate a tabbed interface. Use them to create tabbable regions with our tab JavaScript plugin.

Navs - 图7

  1. <ul class="nav nav-tabs">
  2.   <li class="nav-item">
  3.     <a class="nav-link active" href="#">Active</a>
  4.   </li>
  5.   <li class="nav-item">
  6.     <a class="nav-link" href="#">Link</a>
  7.   </li>
  8.   <li class="nav-item">
  9.     <a class="nav-link" href="#">Link</a>
  10.   </li>
  11.   <li class="nav-item">
  12.     <a class="nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Disabled</a>
  13.   </li>
  14. </ul>

Pills

Take that same HTML, but use .nav-pills instead:

Navs - 图8

  1. <ul class="nav nav-pills">
  2.   <li class="nav-item">
  3.     <a class="nav-link active" href="#">Active</a>
  4.   </li>
  5.   <li class="nav-item">
  6.     <a class="nav-link" href="#">Link</a>
  7.   </li>
  8.   <li class="nav-item">
  9.     <a class="nav-link" href="#">Link</a>
  10.   </li>
  11.   <li class="nav-item">
  12.     <a class="nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Disabled</a>
  13.   </li>
  14. </ul>

Fill and justify

Force your .nav’s contents to extend the full available width one of two modifier classes. To proportionately fill all available space with your .nav-items, use .nav-fill. Notice that all horizontal space is occupied, but not every nav item has the same width.

Navs - 图9

  1. <ul class="nav nav-pills nav-fill">
  2.   <li class="nav-item">
  3.     <a class="nav-link active" href="#">Active</a>
  4.   </li>
  5.   <li class="nav-item">
  6.     <a class="nav-link" href="#">Much longer nav link</a>
  7.   </li>
  8.   <li class="nav-item">
  9.     <a class="nav-link" href="#">Link</a>
  10.   </li>
  11.   <li class="nav-item">
  12.     <a class="nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Disabled</a>
  13.   </li>
  14. </ul>

When using a <nav>-based navigation, be sure to include .nav-item on the anchors.

Navs - 图10

  1. <nav class="nav nav-pills nav-fill">
  2.   <a class="nav-item nav-link active" href="#">Active</a>
  3.   <a class="nav-item nav-link" href="#">Much longer nav link</a>
  4.   <a class="nav-item nav-link" href="#">Link</a>
  5.   <a class="nav-item nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Disabled</a>
  6. </nav>

For equal-width elements, use .nav-justified. All horizontal space will be occupied by nav links, but unlike the .nav-fill above, every nav item will be the same width.

Navs - 图11

  1. <ul class="nav nav-pills nav-justified">
  2.   <li class="nav-item">
  3.     <a class="nav-link active" href="#">Active</a>
  4.   </li>
  5.   <li class="nav-item">
  6.     <a class="nav-link" href="#">Much longer nav link</a>
  7.   </li>
  8.   <li class="nav-item">
  9.     <a class="nav-link" href="#">Link</a>
  10.   </li>
  11.   <li class="nav-item">
  12.     <a class="nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Disabled</a>
  13.   </li>
  14. </ul>

Similar to the .nav-fill example using a <nav>-based navigation, be sure to include .nav-item on the anchors.

Navs - 图12

  1. <nav class="nav nav-pills nav-justified">
  2.   <a class="nav-item nav-link active" href="#">Active</a>
  3.   <a class="nav-item nav-link" href="#">Much longer nav link</a>
  4.   <a class="nav-item nav-link" href="#">Link</a>
  5.   <a class="nav-item nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Disabled</a>
  6. </nav>

Working with flex utilities

If you need responsive nav variations, consider using a series of flexbox utilities. While more verbose, these utilities offer greater customization across responsive breakpoints. In the example below, our nav will be stacked on the lowest breakpoint, then adapt to a horizontal layout that fills the available width starting from the small breakpoint.

Navs - 图13

  1. <nav class="nav nav-pills flex-column flex-sm-row">
  2.   <a class="flex-sm-fill text-sm-center nav-link active" href="#">Active</a>
  3.   <a class="flex-sm-fill text-sm-center nav-link" href="#">Longer nav link</a>
  4.   <a class="flex-sm-fill text-sm-center nav-link" href="#">Link</a>
  5.   <a class="flex-sm-fill text-sm-center nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Disabled</a>
  6. </nav>

Regarding accessibility

If you’re using navs to provide a navigation bar, be sure to add a role="navigation" to the most logical parent container of the <ul>, or wrap a <nav> element around the whole navigation. Do not add the role to the <ul> itself, as this would prevent it from being announced as an actual list by assistive technologies.

Note that navigation bars, even if visually styled as tabs with the .nav-tabs class, should not be given role="tablist", role="tab" or role="tabpanel" attributes. These are only appropriate for dynamic tabbed interfaces, as described in the WAI ARIA Authoring Practices. See JavaScript behavior for dynamic tabbed interfaces in this section for an example.

Using dropdowns

Add dropdown menus with a little extra HTML and the dropdowns JavaScript plugin.

Tabs with dropdowns

Navs - 图14

  1. <ul class="nav nav-tabs">
  2.   <li class="nav-item">
  3.     <a class="nav-link active" href="#">Active</a>
  4.   </li>
  5.   <li class="nav-item dropdown">
  6.     <a class="nav-link dropdown-toggle" data-toggle="dropdown" href="#" role="button" aria-haspopup="true" aria-expanded="false">Dropdown</a>
  7.     <div class="dropdown-menu">
  8.       <a class="dropdown-item" href="#">Action</a>
  9.       <a class="dropdown-item" href="#">Another action</a>
  10.       <a class="dropdown-item" href="#">Something else here</a>
  11.       <div class="dropdown-divider"></div>
  12.       <a class="dropdown-item" href="#">Separated link</a>
  13.     </div>
  14.   </li>
  15.   <li class="nav-item">
  16.     <a class="nav-link" href="#">Link</a>
  17.   </li>
  18.   <li class="nav-item">
  19.     <a class="nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Disabled</a>
  20.   </li>
  21. </ul>

Pills with dropdowns

Navs - 图15

  1. <ul class="nav nav-pills">
  2.   <li class="nav-item">
  3.     <a class="nav-link active" href="#">Active</a>
  4.   </li>
  5.   <li class="nav-item dropdown">
  6.     <a class="nav-link dropdown-toggle" data-toggle="dropdown" href="#" role="button" aria-haspopup="true" aria-expanded="false">Dropdown</a>
  7.     <div class="dropdown-menu">
  8.       <a class="dropdown-item" href="#">Action</a>
  9.       <a class="dropdown-item" href="#">Another action</a>
  10.       <a class="dropdown-item" href="#">Something else here</a>
  11.       <div class="dropdown-divider"></div>
  12.       <a class="dropdown-item" href="#">Separated link</a>
  13.     </div>
  14.   </li>
  15.   <li class="nav-item">
  16.     <a class="nav-link" href="#">Link</a>
  17.   </li>
  18.   <li class="nav-item">
  19.     <a class="nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Disabled</a>
  20.   </li>
  21. </ul>

JavaScript behavior

Use the tab JavaScript plugin—include it individually or through the compiled bootstrap.js file—to extend our navigational tabs and pills to create tabbable panes of local content, even via dropdown menus.

If you’re building our JavaScript from source, it requires util.js.

Dynamic tabbed interfaces, as described in the WAI ARIA Authoring Practices, require role="tablist", role="tab", role="tabpanel", and additional aria- attributes in order to convey their structure, functionality and current state to users of assistive technologies (such as screen readers).

Note that dynamic tabbed interfaces should not contain dropdown menus, as this causes both usability and accessibility issues. From a usability perspective, the fact that the currently displayed tab’s trigger element is not immediately visible (as it’s inside the closed dropdown menu) can cause confusion. From an accessibility point of view, there is currently no sensible way to map this sort of construct to a standard WAI ARIA pattern, meaning that it cannot be easily made understandable to users of assistive technologies.

Navs - 图16

  1. <ul class="nav nav-tabs" id="myTab" role="tablist">
  2.   <li class="nav-item" role="presentation">
  3.     <a class="nav-link active" id="home-tab" data-toggle="tab" href="#home" role="tab" aria-controls="home" aria-selected="true">Home</a>
  4.   </li>
  5.   <li class="nav-item" role="presentation">
  6.     <a class="nav-link" id="profile-tab" data-toggle="tab" href="#profile" role="tab" aria-controls="profile" aria-selected="false">Profile</a>
  7.   </li>
  8.   <li class="nav-item" role="presentation">
  9.     <a class="nav-link" id="contact-tab" data-toggle="tab" href="#contact" role="tab" aria-controls="contact" aria-selected="false">Contact</a>
  10.   </li>
  11. </ul>
  12. <div class="tab-content" id="myTabContent">
  13.   <div class="tab-pane fade show active" id="home" role="tabpanel" aria-labelledby="home-tab">...</div>
  14.   <div class="tab-pane fade" id="profile" role="tabpanel" aria-labelledby="profile-tab">...</div>
  15.   <div class="tab-pane fade" id="contact" role="tabpanel" aria-labelledby="contact-tab">...</div>
  16. </div>

To help fit your needs, this works with <ul>-based markup, as shown above, or with any arbitrary “roll your own” markup. Note that if you’re using <nav>, you shouldn’t add role="tablist" directly to it, as this would override the element’s native role as a navigation landmark. Instead, switch to an alternative element (in the example below, a simple <div>) and wrap the <nav> around it.

Navs - 图17

  1. <nav>
  2.   <div class="nav nav-tabs" id="nav-tab" role="tablist">
  3.     <a class="nav-item nav-link active" id="nav-home-tab" data-toggle="tab" href="#nav-home" role="tab" aria-controls="nav-home" aria-selected="true">Home</a>
  4.     <a class="nav-item nav-link" id="nav-profile-tab" data-toggle="tab" href="#nav-profile" role="tab" aria-controls="nav-profile" aria-selected="false">Profile</a>
  5.     <a class="nav-item nav-link" id="nav-contact-tab" data-toggle="tab" href="#nav-contact" role="tab" aria-controls="nav-contact" aria-selected="false">Contact</a>
  6.   </div>
  7. </nav>
  8. <div class="tab-content" id="nav-tabContent">
  9.   <div class="tab-pane fade show active" id="nav-home" role="tabpanel" aria-labelledby="nav-home-tab">...</div>
  10.   <div class="tab-pane fade" id="nav-profile" role="tabpanel" aria-labelledby="nav-profile-tab">...</div>
  11.   <div class="tab-pane fade" id="nav-contact" role="tabpanel" aria-labelledby="nav-contact-tab">...</div>
  12. </div>

The tabs plugin also works with pills.

Navs - 图18

  1. <ul class="nav nav-pills mb-3" id="pills-tab" role="tablist">
  2.   <li class="nav-item" role="presentation">
  3.     <a class="nav-link active" id="pills-home-tab" data-toggle="pill" href="#pills-home" role="tab" aria-controls="pills-home" aria-selected="true">Home</a>
  4.   </li>
  5.   <li class="nav-item" role="presentation">
  6.     <a class="nav-link" id="pills-profile-tab" data-toggle="pill" href="#pills-profile" role="tab" aria-controls="pills-profile" aria-selected="false">Profile</a>
  7.   </li>
  8.   <li class="nav-item" role="presentation">
  9.     <a class="nav-link" id="pills-contact-tab" data-toggle="pill" href="#pills-contact" role="tab" aria-controls="pills-contact" aria-selected="false">Contact</a>
  10.   </li>
  11. </ul>
  12. <div class="tab-content" id="pills-tabContent">
  13.   <div class="tab-pane fade show active" id="pills-home" role="tabpanel" aria-labelledby="pills-home-tab">...</div>
  14.   <div class="tab-pane fade" id="pills-profile" role="tabpanel" aria-labelledby="pills-profile-tab">...</div>
  15.   <div class="tab-pane fade" id="pills-contact" role="tabpanel" aria-labelledby="pills-contact-tab">...</div>
  16. </div>

And with vertical pills.

Navs - 图19

  1. <div class="row">
  2.   <div class="col-3">
  3.     <div class="nav flex-column nav-pills" id="v-pills-tab" role="tablist" aria-orientation="vertical">
  4.       <a class="nav-link active" id="v-pills-home-tab" data-toggle="pill" href="#v-pills-home" role="tab" aria-controls="v-pills-home" aria-selected="true">Home</a>
  5.       <a class="nav-link" id="v-pills-profile-tab" data-toggle="pill" href="#v-pills-profile" role="tab" aria-controls="v-pills-profile" aria-selected="false">Profile</a>
  6.       <a class="nav-link" id="v-pills-messages-tab" data-toggle="pill" href="#v-pills-messages" role="tab" aria-controls="v-pills-messages" aria-selected="false">Messages</a>
  7.       <a class="nav-link" id="v-pills-settings-tab" data-toggle="pill" href="#v-pills-settings" role="tab" aria-controls="v-pills-settings" aria-selected="false">Settings</a>
  8.     </div>
  9.   </div>
  10.   <div class="col-9">
  11.     <div class="tab-content" id="v-pills-tabContent">
  12.       <div class="tab-pane fade show active" id="v-pills-home" role="tabpanel" aria-labelledby="v-pills-home-tab">...</div>
  13.       <div class="tab-pane fade" id="v-pills-profile" role="tabpanel" aria-labelledby="v-pills-profile-tab">...</div>
  14.       <div class="tab-pane fade" id="v-pills-messages" role="tabpanel" aria-labelledby="v-pills-messages-tab">...</div>
  15.       <div class="tab-pane fade" id="v-pills-settings" role="tabpanel" aria-labelledby="v-pills-settings-tab">...</div>
  16.     </div>
  17.   </div>
  18. </div>

Using data attributes

You can activate a tab or pill navigation without writing any JavaScript by simply specifying data-toggle="tab" or data-toggle="pill" on an element. Use these data attributes on .nav-tabs or .nav-pills.

  1. <!-- Nav tabs -->
  2. <ul class="nav nav-tabs" id="myTab" role="tablist">
  3.   <li class="nav-item" role="presentation">
  4.     <a class="nav-link active" id="home-tab" data-toggle="tab" href="#home" role="tab" aria-controls="home" aria-selected="true">Home</a>
  5.   </li>
  6.   <li class="nav-item" role="presentation">
  7.     <a class="nav-link" id="profile-tab" data-toggle="tab" href="#profile" role="tab" aria-controls="profile" aria-selected="false">Profile</a>
  8.   </li>
  9.   <li class="nav-item" role="presentation">
  10.     <a class="nav-link" id="messages-tab" data-toggle="tab" href="#messages" role="tab" aria-controls="messages" aria-selected="false">Messages</a>
  11.   </li>
  12.   <li class="nav-item" role="presentation">
  13.     <a class="nav-link" id="settings-tab" data-toggle="tab" href="#settings" role="tab" aria-controls="settings" aria-selected="false">Settings</a>
  14.   </li>
  15. </ul>
  17. <!-- Tab panes -->
  18. <div class="tab-content">
  19.   <div class="tab-pane active" id="home" role="tabpanel" aria-labelledby="home-tab">...</div>
  20.   <div class="tab-pane" id="profile" role="tabpanel" aria-labelledby="profile-tab">...</div>
  21.   <div class="tab-pane" id="messages" role="tabpanel" aria-labelledby="messages-tab">...</div>
  22.   <div class="tab-pane" id="settings" role="tabpanel" aria-labelledby="settings-tab">...</div>
  23. </div>

Via JavaScript

Enable tabbable tabs via JavaScript (each tab needs to be activated individually):

  1. $('#myTab a').on('click', function (e) {
  2.   e.preventDefault()
  3.   $(this).tab('show')
  4. })

You can activate individual tabs in several ways:

  1. $('#myTab a[href="#profile"]').tab('show') // Select tab by name
  2. $('#myTab li:first-child a').tab('show') // Select first tab
  3. $('#myTab li:last-child a').tab('show') // Select last tab
  4. $('#myTab li:nth-child(3) a').tab('show') // Select third tab

Fade effect

To make tabs fade in, add .fade to each .tab-pane. The first tab pane must also have .show to make the initial content visible.

  1. <div class="tab-content">
  2.   <div class="tab-pane fade show active" id="home" role="tabpanel" aria-labelledby="home-tab">...</div>
  3.   <div class="tab-pane fade" id="profile" role="tabpanel" aria-labelledby="profile-tab">...</div>
  4.   <div class="tab-pane fade" id="messages" role="tabpanel" aria-labelledby="messages-tab">...</div>
  5.   <div class="tab-pane fade" id="settings" role="tabpanel" aria-labelledby="settings-tab">...</div>
  6. </div>

Methods

Asynchronous methods and transitions

All API methods are asynchronous and start a transition. They return to the caller as soon as the transition is started but before it ends. In addition, a method call on a transitioning component will be ignored.

See our JavaScript documentation for more information.

$().tab

Activates a tab element and content container. Tab should have either a data-target or an href targeting a container node in the DOM.

  1. <ul class="nav nav-tabs" id="myTab" role="tablist">
  2.   <li class="nav-item" role="presentation">
  3.     <a class="nav-link active" id="home-tab" data-toggle="tab" href="#home" role="tab" aria-controls="home" aria-selected="true">Home</a>
  4.   </li>
  5.   <li class="nav-item" role="presentation">
  6.     <a class="nav-link" id="profile-tab" data-toggle="tab" href="#profile" role="tab" aria-controls="profile" aria-selected="false">Profile</a>
  7.   </li>
  8.   <li class="nav-item" role="presentation">
  9.     <a class="nav-link" id="messages-tab" data-toggle="tab" href="#messages" role="tab" aria-controls="messages" aria-selected="false">Messages</a>
  10.   </li>
  11.   <li class="nav-item" role="presentation">
  12.     <a class="nav-link" id="settings-tab" data-toggle="tab" href="#settings" role="tab" aria-controls="settings" aria-selected="false">Settings</a>
  13.   </li>
  14. </ul>
  16. <div class="tab-content">
  17.   <div class="tab-pane active" id="home" role="tabpanel" aria-labelledby="home-tab">...</div>
  18.   <div class="tab-pane" id="profile" role="tabpanel" aria-labelledby="profile-tab">...</div>
  19.   <div class="tab-pane" id="messages" role="tabpanel" aria-labelledby="messages-tab">...</div>
  20.   <div class="tab-pane" id="settings" role="tabpanel" aria-labelledby="settings-tab">...</div>
  21. </div>
  23. <script>
  24.   $(function () {
  25.     $('#myTab li:last-child a').tab('show')
  26.   })
  27. </script>

.tab(‘show’)

Selects the given tab and shows its associated pane. Any other tab that was previously selected becomes unselected and its associated pane is hidden. Returns to the caller before the tab pane has actually been shown (i.e. before the shown.bs.tab event occurs).

  1. $('#someTab').tab('show')

.tab(‘dispose’)

Destroys an element’s tab.

Events

When showing a new tab, the events fire in the following order:

  1. hide.bs.tab (on the current active tab)
  2. show.bs.tab (on the to-be-shown tab)
  3. hidden.bs.tab (on the previous active tab, the same one as for the hide.bs.tab event)
  4. shown.bs.tab (on the newly-active just-shown tab, the same one as for the show.bs.tab event)

If no tab was already active, then the hide.bs.tab and hidden.bs.tab events will not be fired.

Event TypeDescription
show.bs.tabThis event fires on tab show, but before the new tab has been shown. Use event.target and event.relatedTarget to target the active tab and the previous active tab (if available) respectively.
shown.bs.tabThis event fires on tab show after a tab has been shown. Use event.target and event.relatedTarget to target the active tab and the previous active tab (if available) respectively.
hide.bs.tabThis event fires when a new tab is to be shown (and thus the previous active tab is to be hidden). Use event.target and event.relatedTarget to target the current active tab and the new soon-to-be-active tab, respectively.
hidden.bs.tabThis event fires after a new tab is shown (and thus the previous active tab is hidden). Use event.target and event.relatedTarget to target the previous active tab and the new active tab, respectively.
  1. $('a[data-toggle="tab"]').on('shown.bs.tab', function (e) {
  2.   e.target // newly activated tab
  3.   e.relatedTarget // previous active tab
  4. })