Slideshow

Slideshow with a simple crossfade transition
Mountain lake Terraced farm Winter trees Forest river Red panda
Demo: A basic slideshow

Overview

By default the slideshow will immediately begin playing when it is connected to the document, and then advance every 3 seconds.

This component provides no interactivity of its own. For an interactive version, see SlideshowWithPlayControls or CarouselSlideshow. To incorporate slideshow behavior into a component of your own, apply TimerSelectionMixin.

API

Ancestry: Slideshow → CrossfadeStageModesReactiveElement → HTMLElement

Built with mixins AttributeMarshallingMixin, EffectMixin, ReactiveMixin, RenderUpdatesMixin, ShadowTemplateMixin, SingleSelectionMixin, SlotItemsMixin, and TimerSelectionMixin.

Extended by class SlideshowWithPlayControls.

$ 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

canSelectNext property

True if the selection can be moved to the next item, false if not (the selected item is the last item in the list).

Type: boolean

Defined by SingleSelectionMixin

canSelectPrevious property

True if the selection can be moved to the previous item, false if not (the selected item is the first one in the list).

Type: boolean

Defined by SingleSelectionMixin

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

itemCalcs(item, index) method

Returns a set of calculations about the given item that can be derived from the component's current state.

The goal of the itemCalcs step is to ensure that all mixins/classes use a consistent definition for facts about an item that can be derived from component state. By default, itemCalcs includes a member index containing the index of the indicated item. Other mixins/classes can extend the result of itemCalcs to include additional facts.

For example, the SingleSelectionMixin tracks selection at the component level through a state member state.selectedIndex. When rendering a specific item, a component generally wants to know, "Is this specific item the one which is selected?". SingleSelectionMixin does this with a defintion for itemCalcs that looks like this:

itemCalcs(item, index) {
  const base = super.itemCalcs ? super.itemCalcs(item, index) : null;
  return Object.assign({}, base, {
    selected: index === this.selectedIndex
  });
}

This ensures that any other aspect of the component that wants to inspect the selected state of a given item uses a consistent definition for selection.

Parameters:

  • item: Elementthe item being considered
  • index: numberthe item's position in the list

Defined by ContentItemsMixin

items property

The current set of items drawn from the element's current state.

Defined by ContentItemsMixin

itemUpdates(item, calcs, original) method

Determine what updates should be applied to an item to reflect the current state, using the format defined by the updates helpers.

By default, this returns an empty object. You should override this method (or use mixins that override this method) to indicate what updates should be applied to the given item during rendering.

Example: AriaListMixin uses code similar to the following to have an item's aria-selected attribute reflect its selection state:

itemUpdates(item, calcs, original) {
  const base = super.itemUpdates ? super.itemUpdates(item, calcs, original) : {};
  return merge(base, {
    attributes: {
      'aria-selected': calcs.selected
    },
  });
}

This code fragment is intended for use with SingleSelectionMixin, which provides the calcs.selected member.

Parameters:

  • item: Elementthe item to be updated
  • calcs: objectper-item calculations derived from element state
  • original: objectthe item's original HTML attributes, classes, and style

Returns: object the DOM updates that should be applied to the item

Defined by ContentItemsMixin

pause() method

Pause automatic progression of the selection.

Defined by TimerSelectionMixin

play() method

Begin automatic progression of the selection.

Defined by TimerSelectionMixin

playing property

True if the element is playing.

Type: boolean

Default: false

Defined by TimerSelectionMixin

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.

Parameters:

  • 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

selected-index-changed event

Raised when the selectedIndex property changes.

Defined by SingleSelectionMixin

selectedIndex property

The index of the currently-selected item, or -1 if no item is selected.

Type: number

Defined by SingleSelectionMixin

selectedItem property

The currently-selected item, or null if no item is selected.

Type: Element

Defined by SingleSelectionMixin

selectFirst() method

Select the first item in the list.

Returns: Boolean True if the selection changed, false if not.

Defined by SingleSelectionMixin

selectionRequired property

True if the list should always have a selection (if it has items).

Type: boolean

Default: false

Defined by SingleSelectionMixin

selectionTimerDuration property

The time in milliseconds that will elapse after the selection changes before the selection will be advanced to the next item in the list.

Type: number

Default: 1000 (1 second)

Defined by TimerSelectionMixin

selectionWraps property

True if selection navigations wrap from last to first, and vice versa.

Type: boolean

Default: false

Defined by SingleSelectionMixin

selectLast() method

Select the last item in the list.

Returns: Boolean True if the selection changed, false if not.

Defined by SingleSelectionMixin

selectNext() method

Select the next item in the list.

If the list has no selection, the first item will be selected.

Returns: Boolean True if the selection changed, false if not.

Defined by SingleSelectionMixin

selectPrevious() method

Select the previous item in the list.

If the list has no selection, the last item will be selected.

Returns: Boolean True if the selection changed, false if not.

Defined by SingleSelectionMixin

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.

Parameters:

  • 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.

Parameters:

  • nextState: objectthe proposed new state for the element

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

Defined by ReactiveMixin

state property

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

Type: object

Defined by ReactiveMixin

symbols.contentSlot property

Defined by SlotContentMixin

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