SlidingCarousel

A typical carousel with a sliding effect, left/right arrow buttons, and page dots.

Lake Horses Ladybug on wheat Mountain Palm tree
Demo: Sliding carousel

The user can move between items with touch, the mouse, the keyboard, or a trackpad. For a carousel that supports the same types of navigation, but without arrows or dots, see SlidingPages.

SlidingCarousel uses a SlidingViewport to render the items. The left/right arrow buttons are provided by ArrowDirectionMixin, and the small dots at the bottom of the carousel are provided by PageDotsMixin. It's possible to wrap SlidingViewport with just arrows (if you don't want dots) or just page dots (if you don't want arrow buttons); see the demos of those mixins for examples.

SlidingCarousel incorporates LanguageDirectionMixin so that it can flip the order of items in right-to-left languages. See that page for a demonstration.

Usage

import SlidingCarousel from 'elix/src/SlidingCarousel.js';
const slidingCarousel = new SlidingCarousel(); // or
const slidingCarousel = document.createElement('elix-sliding-carousel');

In HTML:

<script type="module" src="node_modules/elix/src/SlidingCarousel.js"></script>
<elix-sliding-carousel>
  <!-- Carousel items such as img elements go here. -->
</elix-sliding-carousel>

SlidingCarousel is appropriate when:

  • You want to present to the user a collection of images, or a mixture of graphical and textual content.
  • You want to let the user focus on a single item at a time.
  • The number of items is small (2–10). The PageDotsMixin will create a PageDot for each item, which would be unweildy for larger collections. If you have a large collection of images to show, it might be better to use SlidingPages, or create your own component that uses ArrowDirectionMixin but not PageDotsMixin.

API

$ 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

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 inherited from ElementBase

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.state.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.

This function invokes itemsForState to extract the items from the element's state.

Defined by ContentItemsMixin

itemsForState(state) method

Given an element state (which might be its current state, or some other hypothetical state), return the items from that state.

By default, this inspects the state member state.content, then uses the helper function content.substantiveElements to subtract out any nodes that would not normally be visible to the user. You can override this to provide an alternative mapping of state to items.

Returns: Array.<Element> the items for the indicated state

Parameters:
  • state: objectthe element state to extract items from

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.

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

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

Defined by ContentItemsMixin

pageDots property

Returns a collection of elements that can be used as page dots.

By default, this creates a PageDot element for each item in the element's items property.

Defined by PageDotsMixin

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

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

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.

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

Parameters:
  • 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)

Parameters:
  • 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

symbols.canGoLeft property

Returns true if it's currently possible to go left.

Type: boolean

Defined by DirectionSelectionMixin

symbols.canGoRight property

Returns true if it's currently possible to go right.

Type: boolean

Defined by DirectionSelectionMixin

symbols.goDown() method

Invokes selectNext to select the next item.

Defined by DirectionSelectionMixin

symbols.goDown() method

Invoked when the user wants to go/navigate down. The default implementation of this method does nothing.

Defined by KeyboardDirectionMixin

symbols.goEnd() method

Invoked when the user wants to go/navigate to the end (e.g., of a list). The default implementation of this method does nothing.

Defined by KeyboardDirectionMixin

symbols.goEnd() method

Invokes selectLast to select the next item.

Defined by DirectionSelectionMixin

symbols.goLeft() method

Invokes selectPrevious to select the previous item.

If the element has a rightToLeft property and it is true, then this selects the next item.

Defined by DirectionSelectionMixin

symbols.goLeft() method

Invoked when the user wants to go/navigate left. The default implementation of this method does nothing.

Defined by KeyboardDirectionMixin

symbols.goRight() method

Invoked when the user wants to go/navigate right. The default implementation of this method does nothing.

Defined by KeyboardDirectionMixin

symbols.goRight() method

Invokes selectNext to select the next item.

If the element has a rightToLeft property and it is true, then this selects the previous item.

Defined by DirectionSelectionMixin

symbols.goStart() method

Invokes selectFirst to select the first item.

Defined by DirectionSelectionMixin

symbols.goStart() method

Invoked when the user wants to go/navigate to the start (e.g., of a list). The default implementation of this method does nothing.

Defined by KeyboardDirectionMixin

symbols.goUp() method

Invokes selectPrevious to select the previous item.

Defined by DirectionSelectionMixin

symbols.goUp() method

Invoked when the user wants to go/navigate up. The default implementation of this method does nothing.

Defined by KeyboardDirectionMixin

symbols.keydown() method

See the symbols documentation for details.

Defined by KeyboardMixin

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

wrap(template) static method

Wrap a base template with left/right arrow buttons.

Call this method in a components symbols.template property to add left/right arrow buttons.

Note: The wrap method hangs off of ArrowDirectionMixin like a static method; the mixin does not add it to an element's prototype chain. Accordingly, you must invoke this method as ArrowDirectionMixin.wrap(template), not this.wrap(template).

Returns: string a template that includes left/right arrow buttons

Parameters:
  • template: stringfor the element(s) controlled by the arrow buttons

Defined by ArrowDirectionMixin

wrap(template) static method

Wrap a base template with page dots.

Call this method in a components symbols.template property to add page dots.

Note: The wrap method hangs off of PageDotsMixin like a static method; the mixin does not add it to an element's prototype chain. Accordingly, you must invoke this method as PageDotsMixin.wrap(template), not this.wrap(template).

Returns: string a template that includes page dots

Parameters:
  • template: stringfor the element(s) controlled by the arrow buttons

Defined by PageDotsMixin

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