A combobox is a widget that includes a text input that controls a listbox of options.
While the term "dropdown" generally refers to an element that reveals a related panel, in the dropdown combobox component the panel is primarily triggered by a text input, although it can be accompanied by a button that also opens the panel.
When to use
- Use a combobox to toggle and search through a listbox of single or multiselect options (
role="option") that don't require a form submission to take effect.
When not to use
- If a user is selecting a single text option from a group of options within a form, consider using a
<select>element, radio group, or checkboxes instead.
- If you need a way for a user to expand or collapse a content section, use an accordion instead.
- The text input can use autocomplete capability that filters the available options. In addition to selecting an option, typing also populates the input with the choice.
- By default, the dropdown panel that contains the listbox opens below and is aligned to the left of the text input. However, when there isn't enough space in the viewport, the panel uses edge detection to position it above and/or aligned to the right of the text input.
- If the content within the dropdown panel exceeds the maximum height then a scrim (gradient overlay) appears at the bottom of the panel as an overflow affordance. When a user has scrolled to the bottom of the overflowed content the scrim is removed.
- In a single select context when an option is selected, the panel is closed and the control updated.
- In a multiselect context the panel stays open until the user applies the selection. The panel then closes and the changes are visible in the UI.
- All panels can be closed by clicking outside of them, using the esc key, or by focus moving to an element outside of the component.
- A limited amount of options that don't scroll can be fixed at the bottom of a dropdown panel.
Error validation is shown inline and may happen in real-time or on submission if used in a form. Real-time validation should help a user understand and remedy the error if possible.
A validation message should always be visible and not placed in a tooltip. The message is placed directly below the trigger element, similar to form validation, and both are presented in an error state, which changes the text and border color of the trigger element to red.
- Placeholder text in the input should only be used for extra, non-essential information when the input purpose is still understood in its absence; it's not a replacement for a visible label. An exception is the search input, which includes a search icon to further clarify its purpose.
- See the listbox content notes.
- A text input must be clearly labeled and identified.
- See the WAI-ARIA Combobox documentation for more details.
- See the WAI-ARIA Listbox documentation for more details.
- When options in a panel are filtered, a screen reader should announce how many options are now available via
- It should be clear if an option is selected or not.
- Drop-Down Usability: When You Should (and Shouldn’t) Use Them, by Baymard Institute
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