--- layout: docs title: Dropdowns description: Toggle contextual overlays for displaying lists of links and more with the Bootstrap dropdown plugin. group: components toc: true --- ## Overview Dropdowns are toggleable, contextual overlays for displaying lists of links and more. They're made interactive with the included Bootstrap dropdown JavaScript plugin. They're toggled by clicking, not by hovering; this is [an intentional design decision.](http://markdotto.com/2012/02/27/bootstrap-explained-dropdowns/) Dropdowns are built on a third party library, [Popper.js](https://popper.js.org/), which provides dynamic positioning and viewport detection. Be sure to include [popper.min.js]({{ site.cdn.popper }}) before Bootstrap's JavaScript or use `bootstrap.bundle.min.js` / `bootstrap.bundle.js` which contains Popper.js. Popper.js isn't used to position dropdowns in navbars though as dynamic positioning isn't required. If you're building our JavaScript from source, it [requires `util.js`]({{ site.baseurl }}/docs/{{ site.docs_version }}/getting-started/javascript/#util). ## Accessibility The [WAI ARIA](https://www.w3.org/TR/wai-aria/) standard defines an actual [`role="menu"` widget](https://www.w3.org/TR/wai-aria/roles#menu), but this is specific to application-like menus which trigger actions or functions. ARIA menus can only contain menu items, checkbox menu items, radio button menu items, radio button groups, and sub-menus. Bootstrap's dropdowns, on the other hand, are designed to be generic and applicable to a variety of situations and markup structures. For instance, it is possible to create dropdowns that contain additional inputs and form controls, such as search fields or login forms. For this reason, Bootstrap does not expect (nor automatically add) any of the `role` and `aria-` attributes required for true ARIA menus. Authors will have to include these more specific attributes themselves. However, Bootstrap does add built-in support for most standard keyboard menu interactions, such as the ability to move through individual `.dropdown-item` elements using the cursor keys and close the menu with the ESC key. ## Examples Wrap the dropdown's toggle (your button or link) and the dropdown menu within `.dropdown`, or another element that declares `position: relative;`. Dropdowns can be triggered from `` or `
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{% endexample %} And with `` elements: {% example html %}
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{% endexample %} The best part is you can do this with any button variant, too:
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{% endhighlight %} ### Split button dropdowns Similarly, create split button dropdowns with virtually the same markup as single button dropdowns, but with the addition of `.dropdown-toggle-split` for proper spacing around the dropdown caret. We use this extra class to reduce the horizontal `padding` on either side of the caret by 25% and remove the `margin-left` that's added for regular button dropdowns. Those extra changes keep the caret centered in the split button and provide a more appropriately sized hit area next to the main button.
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{% endhighlight %} ## Sizing Button dropdowns work with buttons of all sizes, including default and split dropdown buttons.
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{% endhighlight %} ## Dropup variation Trigger dropdown menus above elements by adding `.dropup` to the parent element.
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{% endhighlight %} ## Dropright variation Trigger dropdown menus at the right of the elements by adding `.dropright` to the parent element.
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{% endhighlight %} ## Dropleft variation Trigger dropdown menus at the left of the elements by adding `.dropleft` to the parent element.
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{% endhighlight %} ## Menu items Historically dropdown menu contents *had* to be links, but that's no longer the case with v4. Now you can optionally use `
{% endexample %} ## Menu alignment By default, a dropdown menu is automatically positioned 100% from the top and along the left side of its parent. Add `.dropdown-menu-right` to a `.dropdown-menu` to right align the dropdown menu. {% callout info %} **Heads up!** Dropdowns are positioned thanks to Popper.js (except when they are contained in a navbar). {% endcallout %} {% example html %}
{% endexample %} ## Menu headers Add a header to label sections of actions in any dropdown menu. {% example html %}
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{% endexample %} ## Menu dividers Separate groups of related menu items with a divider. {% example html %}
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{% endexample %} ## Menu forms Put a form within a dropdown menu, or make it into a dropdown menu, and use [margin or padding utilities]({{ site.baseurl }}/docs/{{ site.docs_version }}/utilities/spacing/) to give it the negative space you require. {% example html %}
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{% endexample %} {% example html %}
{% endexample %} ## Disabled menu items Add `.disabled` to items in the dropdown to **style them as disabled**. {% example html %}
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{% endexample %} ## Usage Via data attributes or JavaScript, the dropdown plugin toggles hidden content (dropdown menus) by toggling the `.show` class on the parent list item. The `data-toggle="dropdown"` attribute is relied on for closing dropdown menus at an application level, so it's a good idea to always use it. {% callout info %} On touch-enabled devices, opening a dropdown adds empty (`$.noop`) `mouseover` handlers to the immediate children of the `` element. This admittedly ugly hack is necessary to work around a [quirk in iOS' event delegation](https://www.quirksmode.org/blog/archives/2014/02/mouse_event_bub.html), which would otherwise prevent a tap anywhere outside of the dropdown from triggering the code that closes the dropdown. Once the dropdown is closed, these additional empty `mouseover` handlers are removed. {% endcallout %} ### Via data attributes Add `data-toggle="dropdown"` to a link or button to toggle a dropdown. {% highlight html %}
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{% endhighlight %} ### Via JavaScript Call the dropdowns via JavaScript: {% highlight js %} $('.dropdown-toggle').dropdown() {% endhighlight %} {% callout info %} ##### `data-toggle="dropdown"` still required Regardless of whether you call your dropdown via JavaScript or instead use the data-api, `data-toggle="dropdown"` is always required to be present on the dropdown's trigger element. {% endcallout %} ### Options Options can be passed via data attributes or JavaScript. For data attributes, append the option name to `data-`, as in `data-offset=""`.
Name Type Default Description
offset number | string | function 0 Offset of the dropdown relative to its target. For more information refer to Popper.js's offset docs.
flip boolean true Allow Dropdown to flip in case of an overlapping on the reference element. For more information refer to Popper.js's flip docs.
boundary string | element 'scrollParent' Overflow constraint boundary of the dropdown menu. Accepts the values of 'viewport', 'window', 'scrollParent', or an HTMLElement reference (JavaScript only). For more information refer to Popper.js's preventOverflow docs.
Note when `boundary` is set to any value other than `'scrollParent'`, the style `position: static` is applied to the `.dropdown` container. ### Methods | Method | Description | | --- | --- | | `$().dropdown('toggle')` | Toggles the dropdown menu of a given navbar or tabbed navigation. | | `$().dropdown('update')` | Updates the position of an element's dropdown. | | `$().dropdown('dispose')` | Destroys an element's dropdown. | ### Events All dropdown events are fired at the `.dropdown-menu`'s parent element and have a `relatedTarget` property, whose value is the toggling anchor element. | Event | Description | | --- | --- | | `show.bs.dropdown` | This event fires immediately when the show instance method is called. | | `shown.bs.dropdown` | This event is fired when the dropdown has been made visible to the user (will wait for CSS transitions, to complete). | | `hide.bs.dropdown` | This event is fired immediately when the hide instance method has been called. | | `hidden.bs.dropdown`| This event is fired when the dropdown has finished being hidden from the user (will wait for CSS transitions, to complete). | {% highlight js %} $('#myDropdown').on('show.bs.dropdown', function () { // do something… }) {% endhighlight %}