Positions a Popup with respect to a source element, usually some form of button.

Below left Below stretch Below right
Above left Above stretch Above right
Demo: A PopupSource positions its popup in relation to the source button

A PopupSource can be used as a starting point for various elements that invoke popups, such as a MenuButton or DropdownList.

Demo: A DropdownList is a specialized form of PopupSource

Opening and closing the popup

By default, a PopupSource allows the user to open the associated popup by tapping it, clicking on it with the primary mouse button, or pressing Space.

By default, the popup will be an instance of Popup, which can be closed by tapping/clicking on the page behind the popup or by pressing Esc.


Ancestry: PopupSource → ReactiveElement → HTMLElement

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

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

Extended by classes DropdownList and MenuButton.

$ property

The collection of references to the elements with IDs 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.

Such references simplify a component's access to its own elements. In exchange, this mixin trades off a one-time cost of querying all elements in the shadow tree instead of paying an ongoing cost to query for an element each time the component wants to inspect or manipulate it.

These shadow element references are established the first time you read the $ property. They are not updated if you subsequently modify the shadow tree yourself (to replace one item with another, to add new items with id attributes, etc.).

Type: object

Defined by ShadowTemplateMixin inherited from ReactiveElement

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

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 closePromiseKey

closed property

True if the element is currently closed.

Type: boolean

Defined by closePromiseKey

closed event

Raised when the component closes.

Defined by closePromiseKey

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 closePromiseKey

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 inherited from ReactiveElement

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

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'

open() method

Open the element (if not already opened).

Defined by closePromiseKey

opened property

True if the element is currently closed.

Type: boolean

Defined by closePromiseKey

opened event

Raised when the component opens.

Defined by closePromiseKey

opened-changed event

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

Defined by closePromiseKey

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'

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

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 inherited from ReactiveElement

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 inherited from ReactiveElement

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 inherited from ReactiveElement

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 inherited from ReactiveElement

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'

state property

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

Type: object

Defined by ReactiveMixin inherited from ReactiveElement

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 focusVisibleChangedListenerKey

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 closePromiseKey

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 inherited from ReactiveElement

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 closePromiseKey