Scrollable Listbox Example

Read This First

The code in this example is not intended for production environments. Before using it for any purpose, read this to understand why.

This is an illustrative example of one way of using ARIA that conforms with the ARIA specification.

There may be support gaps in some browser and assistive technology combinations, especially for mobile/touch devices. Testing code based on this example with assistive technologies is essential before considering use in production systems.
The ARIA and Assistive Technologies Project is developing measurements of assistive technology support for APG examples.
Robust accessibility can be further optimized by choosing implementation patterns that maximize use of semantic HTML and heeding the warning that No ARIA is better than Bad ARIA.

About This Example

The following example implementation of the Listbox Pattern demonstrates a scrollable single-select listbox widget. This widget is functionally similar to an HTML select input where the size attribute has a value greater than one.

Similar examples include:

Example Listboxes with Rearrangeable Options: Examples of both single-select and multi-select listboxes with accompanying toolbars where options can be added, moved, and removed.
Listbox Example with Grouped Options: Single-select listbox with grouped options, similar to an HTML select with optgroup children.

Example

Choose your favorite transuranic element (actinide or transactinide).

Notes

This listbox is scrollable; it has more options than its height can accommodate.

Scrolling only works as expected if the listbox is the options' offsetParent. The example uses position: relative on the listbox to that effect.
When an option is focused that isn't (fully) visible, the listbox's scroll position is updated:
1. If Up Arrow or Down Arrow is pressed, the previous or next option is scrolled into view.
2. If Home or End is pressed, the listbox scrolls all the way to the top or to the bottom.
3. If focusItem is called, the focused option will be scrolled to the top of the view if it was located above it or to the bottom if it was below it.
4. If the mouse is clicked on a partially visible option, it will be scrolled fully into view.
When a fully visible option is focused in any way, no scrolling occurs.
Normal scrolling through any scrolling mechanism (including Page Up and Page Down) works as expected. The scroll position will jump as described for focusItem if a means other than a mouse click is used to change focus after scrolling.

Keyboard Support

The example listboxes on this page implement the following keyboard interface. Other variations and options for the keyboard interface are described in the Keyboard Interaction section of the Listbox Pattern.

Key	Function
`Down Arrow`	Moves focus to and selects the next option.
`Up Arrow`	Moves focus to and selects the previous option.
`Home`	Moves focus to and selects the first option.
`End`	Moves focus to and selects the last option.

Role, Property, State, and Tabindex Attributes

The example listboxes on this page implement the following ARIA roles, states, and properties. Information about other ways of applying ARIA roles, states, and properties is available in the Roles, States, and Properties section of the Listbox Pattern.

Role	Attribute	Element	Usage
`listbox`		`ul`	Identifies the focusable element that has listbox behaviors and contains the listbox options.
	`aria-labelledby="ID_REF"`	`ul`	Refers to the element containing the listbox label.
	`tabindex="0"`	`ul`	Includes the listbox in the page tab sequence.
	`aria-activedescendant="ID_REF"`	`ul`	Tells assistive technologies which of the options, if any, is visually indicated as having keyboard focus. DOM focus remains on the `ul` element and the idref specified for `aria-activedescendant` refers to the `li` element that is visually styled as focused. When navigation keys, such as `Down Arrow`, are pressed, the JavaScript changes the value.
`option`		`li`	Identifies each selectable element containing the name of an option.
	`aria-selected="true"`	`li`	Indicates that the option is selected. Applied to the element with role option that is visually styled as selected. The option with this attribute is always the same as the option that is referenced by aria-activedescendant because it is a single-select listbox where selection follows focus.

JavaScript and CSS Source Code

CSS: listbox.css
Javascript: listbox.js, listbox-scrollable.js, utils.js