A text input paired with a popup that can be used as an alternative to typing
Guinea Pig
Hermit Crab
Demo: Like all combo boxes, AutoCompleteComboBox has a text input and an associated popup


The combo box user interface pattern combines the free-form nature of a text area with the convenience of a popup that can be used to populate the text. The popup can help make the user aware of what kinds of text responses are appropriate, and offer them input controls they can click or tap as an alternative to typing. For example, the popup in variations of ListComboBox is some form of ListBox presenting a list of common text responses.

See also

A combo box that auto-completes the user's input against the list items
A combo box which applies its text input as a filter on its list items
Single-selection list box
A combo box whose popup presents a list of choices
A button that invokes a menu


Ancestry: ComboBox → PopupSourceReactiveElement → HTMLElement

Built with mixins AttributeMarshallingMixin, FocusVisibleMixin, KeyboardMixin, KeyboardMixin, OpenCloseMixin, ReactiveMixin, RenderUpdatesMixin, and ShadowTemplateMixin.

By default, this uses these elements in the following roles:

Extended by classes AutoCompleteComboBox, FilterComboBox, and ListComboBox.

$ property

A convenient shortcut for looking up an element by ID in the component's Shadow DOM subtree.

Example: if component's template contains a shadow element <button id="foo">, you can use the reference this.$.foo to obtain the corresponding button in the component instance's shadow tree. The $ function is simply a shorthand for getElementById, so this.$.foo is the same as this.shadowRoot.getElementById('foo').

Type: object

Defined by ShadowTemplateMixin

backdropRole property

The class, tag, or template used for the optional backdrop element behind the overlay.

This can help focus the user's attention on the overlay content. Additionally, a backdrop can be used to absorb clicks on background page elements. For example, Dialog uses ModalBackdrop as an overlay backdrop in such a way.

Type: function|string|HTMLTemplateElement

Default: Backdrop

Defined by PopupSource

close(closeResult) method

Close the component (if not already closed).

Some components like AlertDialog want to indicate why or how they were closed. To support such scenarios, you can supply a value to the optional closeResult parameter. This closeResult will be made available in the whenClosed promise and the state.closeResult member.


  • closeResult: objectan indication of how or why the element closed

Defined by OpenCloseMixin

closed event

Raised when the component closes.

Defined by OpenCloseMixin

closed property

True if the element is currently closed.

Type: boolean

Defined by OpenCloseMixin

closeFinished property

True if the element has completely closed.

For components not using asynchronous open/close effects, this property returns the same value as the closed property. For elements that have a true value of state.openCloseEffects (e.g., elements using TransitionEffectMixin), this property returns true only if state.effect is "close" and state.effectPhase is "after".

Type: boolean

Defined by OpenCloseMixin

defaultState property

The default state for the component. This can be extended by mixins and classes to provide additional default state.

Type: object

Defined by ReactiveMixin

frameRole property

The class, tag, or template used to contain the popup content.

The frame element can be used to provide a border around the popup content, and to provide visual effects such as a drop-shadow to help distinguish popup content from background page elements.

Type: function|string|HTMLTemplateElement

Default: OverlayFrame

Defined by PopupSource

horizontalAlign property

The alignment of the popup with respect to the source button.

  • start: popup and source are aligned on the leading edge according to the text direction
  • end: popup and source are aligned on the trailing edge according to the text direction
  • left: popup and source are left-aligned
  • right: popup and source are right-aligned
  • `stretch: both left and right edges are aligned

Type: 'start'|'end'|'left'|'right'|'stretch'

Default: 'start'

Defined by PopupSource

inputRole property

The class, tag, or template used to create the input element.

Type: function|string|HTMLTemplateElement

Default: 'input'

open() method

Open the element (if not already opened).

Defined by OpenCloseMixin

opened event

Raised when the component opens.

Defined by OpenCloseMixin

opened property

True if the element is currently opened.

Type: boolean

Defined by OpenCloseMixin

opened-changed event

Raised when the opened/closed state of the component changes.

Defined by OpenCloseMixin

popupPosition property

The preferred direction for the popup.

  • above: popup should appear above the source
  • below: popup should appear below the source

Type: 'above'|'below'

Default: 'below'

Defined by PopupSource

popupRole property

The class, tag, or template used to define the popup.

The popup element is responsible for handling overlay behavior.

Type: function|string|HTMLTemplateElement

Default: Popup

Defined by PopupSource

refineState(state) method

Apply changes to a proposed new state for the component to enforce necessary consistency between state members. See Refining state for details.


  • state: objecta proposed new state for the component

Returns: boolean - true if the state is already acceptable as it is

Defined by ReactiveMixin

render() method

Render the component to the DOM.

This method does nothing if the state has not changed since the last render call.

This method invokes all internal render methods. It then invoked componentDidMount (for first render) or componentDidUpdate (for subsequent renders).

Defined by ReactiveMixin

setState(changes) method

Update the component's state by merging the specified changes on top of the existing state. If the component is connected to the document, and the new state has changed, this returns a promise to asynchronously render the component. Otherwise, this returns a resolved promise.


  • changes: objectthe changes to apply to the element's state

Returns: Promise - resolves when the new state has been rendered

Defined by ReactiveMixin

shouldComponentUpdate(nextState) method

Return true if the component should update.

The default implementation does a shallow check of property values like React's PureComponent. This seems adequate for most web components. You can override this to always return true (like React's base Component class), or to perform more specific, deeper checks for changes in state.


  • nextState: objectthe proposed new state for the element

Returns: boolean - true if the component should update (rerender)

Defined by ReactiveMixin

sourceRole property

The class, tag, or template used for the button (or other element) that will invoke the popup.

Type: function|string|HTMLTemplateElement

Default: 'button'

Defined by PopupSource

state property

The component's current state. The returned state object is immutable. To update it, invoke setState.

Type: object

Defined by ReactiveMixin

suppressFocusVisibility() method

Temporarily suppress visibility of the keyboard focus until the next keydown event.

This can be useful in components like Menu that actively manage where the focus is in response to mouse hover activity. If the user uses the keyboard to invoke a menu, then changes to using the mouse, it can be distracting to see the focus indicator moving as well. In such situations, the component can invoke this method (e.g., in response to mousemove) to temporarily suppress focus visibility.

Defined by FocusVisibleMixin

symbols.keydown() method

See the symbols documentation for details.

Defined by KeyboardMixin

toggle(opened) method

Toggle the open/close state of the element.


  • opened: booleantrue if the element should be opened, false if closed.

Defined by OpenCloseMixin

toggleButtonRole property

The class, tag, or template used to create the button that toggles the popup.

Type: function|string|HTMLTemplateElement

Default: SeamlessButton

updates property

The attributes and properies that should be applied to the component on render. By default, this is an empty plain object. Your mixin or component can extend this to identify the properties to set on the host element or elements in the shadow subtree.

Type: object

Defined by RenderUpdatesMixin

whenClosed() method

This method can be used as an alternative to listening to the "opened-changed" event, particularly in situations where you want to only handle the next time the component is closed.

Returns: Promise A promise that resolves when the element has completely closed, including the completion of any asynchronous opening effect.

Defined by OpenCloseMixin