527f55c2f3
* Offset option can be function (Popper.js) * Fix...add function type for offset option * Remove constants for popper config * Optimize code. Remove foreach loop. * Refactoring. Remove getOffset method
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| layout | title | description | group | toc |
|---|---|---|---|---|
| docs | Dropdowns | Toggle contextual overlays for displaying lists of links and more with the Bootstrap dropdown plugin. | components | 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.
Dropdowns are built on a third party library, Popper.js, 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.
If you're building our JS from source, it [requires util.js]({{ site.baseurl }}/docs/{{ site.docs_version }}/getting-started/javascript/#util).
Accessibility
The WAI ARIA standard defines an actual role="menu" widget, 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 <a> or <button> elements to better fit your potential needs.
Single button dropdowns
Any single .btn can be turned into a dropdown toggle with some markup changes. Here's how you can put them to work with either <button> elements:
{% example html %}
And with <a> elements:
{% example html %}
{% endexample %}The best part is you can do this with any button variant, too:
{% highlight html %}
{% 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.
{% highlight html %}
Sizing
Button dropdowns work with buttons of all sizes, including default and split dropdown buttons.
{% highlight html %}
Dropup variation
Trigger dropdown menus above elements by adding .dropup to the parent element.
{% highlight html %}
Menu items
Historically dropdown menu contents had to be links, but that's no longer the case with v4. Now you can optionally use <button> elements in your dropdowns instead of just <a>s.
{% example html %}
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 %}
Menu headers
Add a header to label sections of actions in any dropdown menu.
{% example html %}
{% endexample %}Menu dividers
Separate groups of related menu items with a divider.
{% example html %}
{% 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 %}
{% endexample %}{% example html %}
Disabled menu items
Add .disabled to items in the dropdown to style them as disabled.
{% example html %}
{% 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 <body> element. This admittedly ugly hack is necessary to work around a quirk in iOS' event delegation, 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 %}
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. |
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. |
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 %}