An enhancement of a textbox
Select phone model item specifics
An enhanced textbox that allows free text input, selection from a predefined list of options, or a combination of both. Hence the name "combobox". It may also optionally have autocomplete behavour.
Updated: May 15th, 2021
- combobox: the pattern as a whole, comprised of the following distinct parts
- textbox: stores and displays the form value
- flyout: the overlay that contains a listbox
- option/suggestion: a suggestion inside of the listbox and/or directly after the textbox value
- autocomplete: the autocomplete type (optional)
- filter: the filtering criteria (optional)
- autoSelect: a combobox with
autoSelectwill automatically select and fill the textbox value when user cycles through listbox options. Otherwise,
ENTERkey is required to manually select an option. Typically autoSelect will be
truefor a combobox with autocomplete behaviour.
Each row in the list of options performs only a singular action: setting the value of the textbox. It is not possible, at the time of writing, to have additional actions per row, e.g. add, edit or delete.
The combobox listbox is not intended for storing or display kind of single-select or multi-select state. Again, the purpose of each option is to simply set the value of the textbox.
A combobox is an enhancement of textbox. Likewise, autocomplete is an enhancement of combobox. Suggestions provided will update dynamically based on user input. The suggested values may appear inline within the textbox, in a list, or both places at once.
Examples of autocomplete are the URL bar in browsers, and the main search field in search engines.
When the combobox receives focus, the listbox should expand to show all options.
With listbox expanded, pressing
UP-ARROWkeys must navigate through the list of options. The keyboard focus will appear to be in two places at the same time - the textbox and the listbox. In actual fact, keyboard focus always stays on the textbox. The aria-activedescendant property controls the pseudo-focus inside of the listbox.
SPACEBARmust always enter a blank space in the textbox.
For a combobox with
autoSelect, changing the highlighted option will automatically fill the textbox with that option.
For a combobox without
autoSelect, changing the highlighted option must not automatically fill the textbox;
ENTERkey is required to manually select the option.
ENTERkey while an option is highlighted must collapse the listbox. For a combobox with
autoSelectthe form will be submitted. For a combobox without
autoSelectthe form must not be submitted.
ESCkey while an option is highlighted must collapse the listbox.
For autocomplete type "list":
The listbox remains but the options change based on the custom filtering criteria.
With focus in the empty combobox, type any letter. Any suggestions that match the filter will appear as options in the listbox flyout.
For autocomplete type "inline":
The listbox is removed. The entire combobox value will update as the user types, with the suggested portion highlighted as a selection range.
For autocomplete type "both":
This section is under development.
The screen reader will announce the input as "text edit", "combobox" or words to those effect, depending on level of ARIA support.
The screen reader will announce "expanded" or "collapsed", depending on level of ARIA support.
The screen reader will announce any additional programmatic description, depending on level of ARIA support.
The screen reader will announce the current value of the textbox.
When the combobox receives focus, via click or tap, the listbox should expand to show all options.
Clicking or tapping an option will fill the textbox with that value and collapse the listbox without triggering a form submit.
We start with a label and textbox.
<span class="combobox" id="combobox-0">
<label for="combobox-0-input">Game Console</label>
<input id="combobox-0-input" name="console" type="text" placeholder="Playstation 4, Xbox One, etc."/>
<!-- listbox options will go here -->
We have added our elements inside of a
A listbox element will be appended to this wrapper. It is up to you whether you wish to render this server-side or client-side. There are pros and cons to both approaches, which we will discuss below.
The listbox may render on the server or the client. It is wise to put the listbox in a hidden state if rendering on the server. To do so, use the
<div class="combobox__overlay" hidden>
<ul id="combobox_0-listbox" role="listbox">
<li role="option" id="nid-0">Playstation 3</li>
<li role="option" id="nid-1">Playstation 4</li>
<li role="option" id="nid-2">Xbox 360</li>
<li role="option" id="nid-3">Xbox One</li>
<li role="option" id="nid-4">Wii</li>
<li role="option" id="nid-5">Wii U</li>
role=combobox. We also create the properties and state that connect the combobox to the listbox:
<input id="combobox-0-input" name="console0" type="text" placeholder="Playstation 4, Xbox One, etc." role="combobox" aria-expanded="false" autocomplete="off" aria-owns="combobox_0-listbox">
The new attributes are
At the time of writing, screen readers don't do a good job of conveying the combobox role or how to interact with it. To solve this problem, we can add a description via
<input aria-roledescription="Use up and down arrow keys to navigate combobox options" id="combobox-0-input" name="console0" type="text" placeholder="Playstation 4, Xbox One, etc." role="combobox" aria-expanded="false" autocomplete="off" aria-owns="combobox_0-listbox">
Now the screen reader announces the description whenever focus lands on the combobox.
If the number of options will change based on the value of the combobox (i.e. filtering occurs), the description should also make the user aware of this:
<input aria-roledescription="Use up and down arrow keys to navigate combobox options. Combobox options may change based on input." id="combobox-0-input" name="console0" type="text" placeholder="Playstation 4, Xbox One, etc." role="combobox" aria-expanded="false" autocomplete="off" aria-owns="combobox_0-listbox"/>
Our elements are now in place, but how does a keyboard user navigate to the options? We cannot use TAB key because focus must stay on the combobox (so that user can type and enter their own value). As with most complex widgets, the answer lies in the arrow keys. Up and down arrow keys are the way to select our combobox options.
If focus must remain on the combobox, how then do we also have focus on the listbox options? The answer is that we don't. Focus always remains on the combobox and instead we have a kind of pseudo-focus on the options.
How does the screen reader know where this pseudo-focus is?
We call the option with pseudo-focus the "active descendant". And guess what, there is an ARIA attribute for this called
aria-activedescendant. This attribute is placed on the combobox element. The attribute value is the ID of the currently active (pseudo-focussed) option. This allows assistive technology such as a screen reader to programmatically determine
To make all of this easier, we recommend using a plugin such as makeup-active-descendant. After your HTML structure is in place, simply initialise the plugin on the widget and up/down arrow keys will update the necessary states. Use CSS to style the active descendant in any way you like.
This section gives an overview of ARIA usage, within the context of this pattern.
This attribute changes the role of the text input from
Gives additional instructions on how to operate the combobox options.
The list of suggestions has a role of listbox.
Each listbox item has a role of option.
This property creates a programmatic hierarchy in the accessibility tree for the combobox and the listbox.
Conveys the expanded state of the combobox.
Provides the expand/collapse button with an accessible label, in the case where it has no visible text (i.e. an icon button).