Editable Combobox With List Autocomplete Example

About This Example

The below combobox for choosing the name of a US state or territory demonstrates the Combobox Pattern. The design pattern describes four types of autocomplete behavior. This example illustrates the autocomplete behavior known as list autocomplete with manual selection. If the user types one or more characters in the edit box and the typed characters match the beginning of the name of one or more states or territories, a listbox popup appears containing the matching names. When the listbox appears, a suggested name is not automatically selected. Thus, after typing, if the user tabs or clicks out of the combobox without choosing a value from the listbox, the typed string becomes the value of the combobox. Note that this implementation enables users to input the name of a state or territory, but it does not prevent input of any other arbitrary value.

Similar examples include:

• Select-Only Combobox: A single-select combobox with no text input that is functionally similar to an HTML select element.
• Editable Combobox with Both List and Inline Autocomplete: An editable combobox that demonstrates the autocomplete behavior known as list with inline autocomplete.
• Editable Combobox Without Autocomplete: An editable combobox that demonstrates the behavior associated with aria-autocomplete=none.
• Editable Combobox with Grid Popup: An editable combobox that presents suggestions in a grid, enabling users to navigate descriptive information about each suggestion.
• Date Picker Combobox: An editable date input combobox that opens a dialog containing a calendar grid and buttons for navigating by month and year.

Accessibility Features

• Browsers do not manage visibility of elements referenced by aria-activedescendant like they do for elements with focus. When a keyboard event changes the active option in the listbox, the JavaScript scrolls the option referenced by aria-activedescendant into view. Managing aria-activedescendant visibility is essential to accessibility for people who use a browser's zoom feature to increase the size of content.
• To enhance perceivability when operating the combobox, visual keyboard focus and hover are styled using the CSS :hover pseudo-class, and focus and blur event handlers:
  • To make it easier to perceive when the combobox receives focus, focus creates a 2 pixel focus ring around both the input and button elements with 2 pixels of space between the focus ring and the combobox.
  • To make it easier to perceive that either the input or button can be clicked to open the listbox, hover causes the same styling as focus.
  • To help people with visual impairments identify the combobox as an interactive element, the cursor is changed to a pointer when hovering over the combobox or list.
  • To make it easier to distinguish the selected listbox option from other options, selection creates a 2 pixel border above and below the option.
  • Note: Because transparent borders are visible on some systems with operating system high contrast settings enabled, transparency cannot be used to create a visual difference between the element that is focused an other elements. Instead of using transparency, the focused element has a thicker border and less padding. When an element receives focus, its border changes from zero to two pixels and padding is reduced by two pixels. When an element loses focus, its border changes from two pixels to two and padding is increased by two pixels.
• To ensure the inline SVG graphic used for the arrow in the open button has sufficient contrast with the background when high contrast settings change the color of text content, CSS forced-color-adjust is set to auto on the svg element and and the fill attribute of the polygon element is set to currentcolor. This causes the colors of the fill of the polygon elements to be overridden by the high contrast color setting. If forced-color-adjust were not used to override the colors specified for the fill property, the color would remain the same in high contrast mode, which could lead to insufficient contrast between the arrow and the background or even make it invisible if the color matched the high contrast mode background.
  Note: The explicit setting of forced-color-adjust is necessary because some browsers do not use auto as the default value for SVG graphics.

Keyboard Support

The example combobox on this page implements the following keyboard interface. Other variations and options for the keyboard interface are described in the Keyboard Interaction section of the Combobox Pattern.

Textbox

Listbox Popup

NOTE: When visual focus is in the listbox, DOM focus remains on the textbox and the value of aria-activedescendant on the textbox is set to a value that refers to the listbox option that is visually indicated as focused. Where the following descriptions of keyboard commands mention focus, they are referring to the visual focus indicator. For more information about this focus management technique, see Managing Focus in Composites Using aria-activedescendant.

Button

The button has been removed from the tab sequence of the page, but is still important to assistive technologies for mobile devices that use touch events to open the list of options.

Role, Property, State, and Tabindex Attributes

The example combobox on this page implements 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 Combobox Pattern.

Textbox

Listbox Popup

Button

JavaScript and CSS Source Code

• CSS: combobox-autocomplete.css
• Javascript: combobox-autocomplete.js

HTML Source Code