` or ``), the attribute `role="button"` should be added to the element.
If your control element is targeting a single collapsible element – i.e., the `data-coreui-target` attribute is pointing to an `id` selector – you should attach the `aria-controls` attribute to the control part, including the `id` of the collapsible element. Modern screen readers and related assistive technologies address this attribute to provide users with extra shortcuts to navigate directly to the collapsible element itself.
Note that CoreUI for Bootstrap's current implementation does not cover the various *optional* keyboard interactions described in the [WAI-ARIA Authoring Practices 1.1 accordion pattern](https://www.w3.org/TR/wai-aria-practices-1.1/#accordion) - you will need to include these yourself with custom JavaScript.
## Usage
The collapse plugin utilizes a few classes to handle the heavy lifting:
- `.collapse` marks the element and never leaves it; without `.show` the content is hidden
- `.collapse.show` shows the content — the class is added when the opening transition starts and removed when the closing one starts
- `.collapsing` is added when either transition starts, and removed when it finishes
These classes can be found in `_transitions.scss`.
### Via data attributes
Just add `data-coreui-toggle="collapse"` and a `data-coreui-target` to the element to automatically assign control of one or more collapsible elements. The `data-coreui-target` attribute accepts a CSS selector to apply the collapse to. Be sure to add the class `collapse` to the collapsible element. If you'd like it to default open, add the additional class `show`.
To add accordion-like group management to a collapsible area, add the data attribute `data-coreui-parent="#selector"`. Refer to the demo to see this in action.
### Via JavaScript
Enable manually with:
```js
const collapseElementList = document.querySelectorAll('.collapse')
const collapseList = [...collapseElementList].map(collapseEl => new coreui.Collapse(collapseEl))
```
### Options
Options can be passed using data attributes or JavaScript. To do this, append an option name to `data-coreui-`, such as `data-coreui-animation="{value}"`. Remember to convert the case of the option name from "_camelCase_" to "_kebab-case_" when using data attributes. For instance, you should write `data-coreui-custom-class="beautifier"` rather than `data-coreui-customClass="beautifier"`.
Starting with CoreUI 4.2.6, all components support an **experimental** reserved data attribute named `data-coreui-config`, which can contain simple component configurations as a JSON string. If an element has attributes `data-coreui-config='{"delay":50, "title":689}'` and `data-coreui-title="Custom Title"`, then the final value for `title` will be `Custom Title`, as the standard data attributes will take precedence over values specified in `data-coreui-config`. Moreover, existing data attributes can also hold JSON values like `data-coreui-delay='{"show":50, "hide":250}'`.
| Name | Type | Default | Description |
| --- | --- | --- | --- |
`hiddenUntilFound` | boolean | `false` | Hides the collapsed content with [`hidden="until-found"`](https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/hidden) instead of taking it out of the layout, so find-in-page can search it and reveal it. |
`parent` | selector, jQuery object, DOM element | `null` | If parent is provided, then all collapsible elements under the specified parent will be closed when this collapsible item is shown. (similar to traditional accordion behavior - this is dependent on the `card` class). The attribute has to be set on the target collapsible area. |
### Methods
> #### Promises and transitions
>
> **Methods that show or hide a component return a promise.** The promise resolves when the transition ends, so `await` continues at the same moment a `shown.coreui.*` or `hidden.coreui.*` listener runs. The methods still return immediately and never block the caller. A call on a component that is already transitioning does nothing and resolves right away.
>
> [Refer to our JavaScript documentation for further details](https://coreui.io/bootstrap/docs/getting-started/javascript/#promises-and-transitions).
Activates your content as a collapsible element. Accepts an optional options `object`.
The constructor keeps the state that your markup declares. Add `.show` to open the element, and leave it off to keep the element closed. Call `show()`, `hide()` or `toggle()` to change the state.
```js
const bsCollapse = new coreui.Collapse('#myCollapse')
bsCollapse.show()
```
| Method | Description |
| --- | --- |
| `dispose` | Destroys an element's collapse. (Removes stored data on the DOM element) |
| `getInstance` | Static method which allows you to get the collapse instance associated to a DOM element, you can use it like this: `coreui.Collapse.getInstance(element)` |
| `getOrCreateInstance` | Static method which returns a collapse instance associated to a DOM element or create a new one in case it wasn't initialized. You can use it like this: `coreui.Collapse.getOrCreateInstance(element)` |
| `hide` | Hides a collapsible element. **Returns a promise that resolves after the collapsible element is hidden** (e.g., after the `hidden.coreui.collapse` event occurs). |
| `show` | Shows a collapsible element. **Returns a promise that resolves after the collapsible element is shown** (e.g., after the `shown.coreui.collapse` event occurs). |
| `toggle` | Toggles a collapsible element to shown or hidden. **Returns a promise that resolves after the collapsible element is shown or hidden** (i.e. after the `shown.coreui.collapse` or `hidden.coreui.collapse` event occurs). |
### Events
CoreUI for Bootstrap's collapse class exposes a few events for hooking into collapse functionality.
| Event type | Description |
| --- | --- |
| `hidden.coreui.collapse` | This event is fired when a collapse element has been hidden from the user (will wait for CSS transitions to complete). |
| `hide.coreui.collapse` | This event is fired immediately when the `hide` method has been called. |
| `show.coreui.collapse` | This event fires immediately when the `show` instance method is called. |
| `shown.coreui.collapse` | This event is fired when a collapse element has been made visible to the user (will wait for CSS transitions to complete). |
```js
const myCollapsible = document.getElementById('myCollapsible')
myCollapsible.addEventListener('hidden.coreui.collapse', event => {
// do something...
})
```
## Customizing
### CSS variables
The three variables are declared on both `.collapse` and `.collapsing`, so overriding them on an ancestor retimes every collapse below it.
`--cui-transition-collapse-property` names what animates. Adding to the animation is one declaration instead of a whole new `transition` — that is how `.collapse-horizontal` switches from `height` to `width`, and how the findable option adds `content-visibility`. Keep `display` in the list: it is what holds the element in the layout until the closing transition ends.
```scss
$collapse-tokens: defaults(
(
--cui-transition-collapse-property: #{"block-size, display"},
--cui-transition-collapse-duration: .35s,
--cui-transition-collapse-timing: ease,
),
$collapse-tokens
);
```
### Classes
Collapse transition classes can be found in `scss/_transitions.scss` as these are shared across multiple components (collapse and accordion).
```scss
// Both classes carry the tokens: `.collapsing` marks a running transition on
// either path, and find-in-page reveals the content with neither toggle
// happening.
.collapse,
.collapsing {
@include tokens($collapse-tokens);
}
// As wide as its content, not as wide as its container: the open size is the
// animation's target, and a target of `auto` would spend most of the run
// growing an empty box past the content.
.collapse-horizontal {
width: fit-content;
}
// The browser animates the size itself: `interpolate-size` lets the `0` of
// the closed state interpolate to the `auto` of the open one, and `display`
// transitions discretely, so the element stays laid out until the size
// reaches `0`.
@supports (interpolate-size: allow-keywords) {
.collapse {
interpolate-size: allow-keywords;
@include transition-props(
var(--cui-transition-collapse-property),
var(--cui-transition-collapse-duration),
var(--cui-transition-collapse-timing),
allow-discrete
);
// `until-found` content is hidden by the browser instead, which keeps it
// laid out so find-in-page can reach it. `display: none` would take it
// back out of the layout and undo that.
&:not(.show, [hidden="until-found"]) {
display: none;
height: 0;
}
// The box is clipped only while the move runs, so a dropdown inside an
// open collapse can still spill out of it.
&.collapsing {
overflow: hidden;
}
// A hidden collapse is not rendered, so the opening side needs a start
// value of its own — but only when JavaScript marks the run: a collapse
// that loads already open must not play an entrance.
&.show.collapsing {
@starting-style {
height: 0;
}
}
&.collapse-horizontal {
--cui-transition-collapse-property: width, display;
&:not(.show, [hidden="until-found"]) {
width: 0;
height: auto;
}
&.show.collapsing {
@starting-style {
width: 0;
}
}
}
}
}
// Everywhere else JavaScript measures the two sizes and the stylesheet still
// times the move between them.
@supports not (interpolate-size: allow-keywords) {
.collapse:not(.show, .collapsing, [hidden="until-found"]) {
display: none;
}
.collapsing {
height: 0;
overflow: hidden;
@include transition-props(
var(--cui-transition-collapse-property),
var(--cui-transition-collapse-duration),
var(--cui-transition-collapse-timing)
);
&.collapse-horizontal {
--cui-transition-collapse-property: width;
width: 0;
height: auto;
}
}
}
```