A simple backdrop for a modal overlay such as a Dialog or Drawer. The backdrop slightly obscures the background elements, focusing the user's attention on the overlay. It also contributes to the modality by absorbing background clicks.

Tap/click here or press Esc to cancel.

This paragraph has a z-index, but should appear behind the dialog. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse sed lorem scelerisque, blandit libero vitae, dapibus nisl. Sed turpis diam, placerat a feugiat sed, maximus at velit. Ut sit amet semper sapien. Donec vitae leo ex. Duis eget quam sed metus tempor lobortis eget feugiat elit. Cras varius, arcu ac commodo tincidunt, lectus dui convallis nunc, quis maximus nisl erat ac mi. Phasellus et velit diam.

Demo: A ModalBackdrop appears behind a Dialog to partially obscure the background


$ 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 ElementBase

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 ElementBase

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 ElementBase

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.

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

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

Defined by ReactiveMixin inherited from ElementBase

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.

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

  • nextState: objectthe proposed new state for the element

Defined by ReactiveMixin inherited from ElementBase

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 ElementBase

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 ElementBase

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