API Documentation

Carousel ⇐ ElementBase

Lets the user navigate laterally through a sequence of child elements.

basic-carousel is an implementation of the carousel user interface pattern, commonly used for navigating between images, pages, and other elements. This pattern presents the user with a linear sequence of elements, only one of which is shown at a time. The user can navigate to the next/previous element with a variety of input methods.

Live demo

The above demo adds the optional basic-arrow-selection and basic-page-dots components. You can also view a plain demo demo.

basic-carousel uses its children as the elements the user will navigate through. In a typical use, a basic-carousel can be used to navigate between a sequence of images:

<basic-carousel>
  <img src="image1.jpg">
  <img src="image2.jpg">
  <img src="image3.jpg">
</basic-carousel>

The child elements can be of any type — they are not restricted to images.

This component attempts to meet the [Gold Standard for web components] (https://github.com/webcomponents/gold-standard/wiki) so that it is generally as flexible and robust as standard HTML elements. For example, it meets the "Content Changes" criteria: the carousel will adapt to new child elements added or removed at runtime.

Currently, this component does not meet the Gold Standard criteria "Size to Content". As a result, for the time being, you must manually set a size on this component. Two approaches are to: 1) stretch the component across whatever surface it is contained within, or 2) set it to be larger than the largest child element you want to display. The former approach is more common, and can be achieved with CSS styling such as:

html {
  height: 100%;
}

body {
  display: -webkit-flex;
  display: flex;
  height: 100%;
  margin: 0;
}

basic-carousel {
  -webkit-flex: 1;
  flex: 1;
}

The standard basic-carousel component supports navigation via the following input methods:

• Keyboard. When the carousel has focus, the user can press Left, Right, Home, or End. These navigate to the expected element.
• Touch. On mobile and other touch-enabled devices, the user can drag left or right.
• Trackpad. The user can swipe left or right on a trackpad to navigate.

Because carousels are used in a wide variety of circumstances, by default basic-carousel provides a minimal appearance and no separately interactive elements such as arrow buttons on the side or dots along the bottom. Those elements can be added by wrapping a basic-carousel in optional accessories:

• basic-arrow-selection. This adds prominent left and right arrow buttons on the side of the carousel.
• basic-page-dots. This adds a series of small dots below the carousel to indicate the user's current position in the sequence.
• basic-slideshow-timer. Advances to the next item on a timer.
• basic-tab-strip. Adds a strip of traditional tab buttons.

See those components for more details, but in general you can construct a common carousel with both arrow buttons and dots like so:

<basic-arrow-selection>
  <basic-page-dots>
    <basic-carousel>
      ... images, etc. ...
    </basic-carousel>
  </basic-page-dots>
</basic-arrow-selection>

For universal access, basic-carousel automatically adds a variety of ARIA properties to itself and to child elements. This helps users navigate the sequence of elements in the carousel using assistive technologies.

Kind: global class Extends: ElementBase
Mixes: ContentAsItems , DirectionSelection , DistributedChildrenAsContent , FractionalSelection , Generic , ItemsSelection , Keyboard , KeyboardDirection , ObserveContentChanges , SelectionAnimation , SelectionAriaActive , SwipeDirection , TargetInCollective , TargetSelection , TrackpadDirection

• Carousel ⇐ ElementBase
  • .applySelection(item, selected)
  • .applySelection(item, selected)
  • .canSelectNext : boolean
  • .canSelectPrevious : boolean
  • .content : Array.<HTMLElement>
  • "content-changed"
  • .contentChanged()
  • .generic : Boolean
  • .goDown()
  • .goEnd()
  • .goLeft()
  • .goLeft()
  • .goLeft()
  • .goRight()
  • .goRight()
  • .goRight()
  • .goStart()
  • .goUp()
  • .itemAdded(item)
  • .itemAdded(item)
  • .items : Array.<HTMLElement>
  • .items : Array.<HTMLElement>
  • "items-changed"
  • .itemsChanged()
  • .itemsChanged()
  • .keydown(event) ⇒ boolean
  • .navigationAxis : string
  • "selected-index-changed"
  • "selected-item-changed"
  • .selectedFraction : number
  • .selectedFraction : number
  • .selectedIndex : number
  • .selectedItem : object
  • .selectedItem : HTMLElement
  • .selectFirst()
  • .selectionAnimationDuration : number
  • .selectionAnimationEffect : string
  • .selectionAnimationKeyframes : Array.<cssRules>
  • .selectionRequired : boolean
  • .selectionWraps : boolean
  • .selectionWraps : boolean
  • .selectLast()
  • .selectNext()
  • .selectPrevious()
  • .showTransition : boolean
  • .target : HTMLElement
  • .target : HTMLElement
  • .travelFraction : number
  • .travelFraction : number

carousel.applySelection(item, selected)

Apply the selection state to a single item.

Invoke this method to signal that the selected state of the indicated item has changed. By default, this applies a selected CSS class if the item is selected, and removed it if not selected.

Kind: instance method of Carousel. Defined by ContentAsItems mixin.

| Param | Type | Description | | --- | --- | --- | | item | HTMLElement | The item whose selection state has changed. | | selected | boolean | True if the item is selected, false if not. |

carousel.applySelection(item, selected)

Apply the indicate selection state to the item.

The default implementation of this method does nothing. User-visible effects will typically be handled by other mixins.

Kind: instance method of Carousel. Defined by ItemsSelection mixin.

| Param | Type | Description | | --- | --- | --- | | item | HTMLElement | the item being selected/deselected | | selected | boolean | true if the item is selected, false if not |

carousel.canSelectNext : boolean

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

Kind: instance property of Carousel. Defined by ItemsSelection mixin.

carousel.canSelectPrevious : boolean

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

Kind: instance property of Carousel. Defined by ItemsSelection mixin.

carousel.content : Array.<HTMLElement>

The content of this component, defined to be the flattened array of children distributed to the component.

Kind: instance property of Carousel. Defined by DistributedChildrenAsContent mixin.

"content-changed"

This event is raised when the component's contents (including distributed children) have changed.

Kind: event emitted by Carousel. Defined by ObserveContentChanges mixin.

carousel.contentChanged()

Invoked when the contents of the component (including distributed children) have changed.

This method is also invoked when a component is first instantiated; the contents have essentially "changed" from being nothing. This allows the component to perform initial processing of its children.

Kind: instance method of Carousel. Defined by ObserveContentChanges mixin.

carousel.generic : Boolean

True if the component would like to receive generic styling.

This property is true by default — set it to false to turn off all generic styles. This makes it easier to apply custom styling; you won't have to explicitly override styling you don't want.

Kind: instance property of Carousel. Defined by Generic mixin. Default: true

carousel.goDown()

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

Kind: instance method of Carousel. Defined by KeyboardDirection mixin.

carousel.goEnd()

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

Kind: instance method of Carousel. Defined by KeyboardDirection mixin.

carousel.goLeft()

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

Kind: instance method of Carousel. Defined by TrackpadDirection mixin.

carousel.goLeft()

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

Kind: instance method of Carousel. Defined by SwipeDirection mixin.

carousel.goLeft()

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

Kind: instance method of Carousel. Defined by KeyboardDirection mixin.

carousel.goRight()

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

Kind: instance method of Carousel. Defined by TrackpadDirection mixin.

carousel.goRight()

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

Kind: instance method of Carousel. Defined by SwipeDirection mixin.

carousel.goRight()

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

Kind: instance method of Carousel. Defined by KeyboardDirection mixin.

carousel.goStart()

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

Kind: instance method of Carousel. Defined by KeyboardDirection mixin.

carousel.goUp()

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

Kind: instance method of Carousel. Defined by KeyboardDirection mixin.

carousel.itemAdded(item)

Handle a new item being added to the list.

The default implementation of this method simply sets the item's selection state to false.

Kind: instance method of Carousel. Defined by ItemsSelection mixin.

| Param | Type | Description | | --- | --- | --- | | item | HTMLElement | the item being added |

carousel.itemAdded(item)

This method is invoked whenever a new item is added to the list.

The default implementation of this method does nothing. You can override this to perform per-item initialization.

Kind: instance method of Carousel. Defined by ContentAsItems mixin.

| Param | Type | Description | | --- | --- | --- | | item | HTMLElement | The item that was added. |

carousel.items : Array.<HTMLElement>

The current set of items in the list.

Kind: instance property of Carousel. Defined by TargetSelection mixin.

carousel.items : Array.<HTMLElement>

The current set of items in the list. See the top-level documentation for mixin for a description of how items differ from plain content.

Kind: instance property of Carousel. Defined by ContentAsItems mixin.

"items-changed"

Fires when the items in the list change.

Kind: event emitted by Carousel. Defined by ContentAsItems mixin.

carousel.itemsChanged()

This method is invoked when the underlying contents change. It is also invoked on component initialization – since the items have "changed" from being nothing.

Kind: instance method of Carousel. Defined by TargetSelection mixin.

carousel.itemsChanged()

This method is invoked when the underlying contents change. It is also invoked on component initialization – since the items have "changed" from being nothing.

Kind: instance method of Carousel. Defined by ContentAsItems mixin.

carousel.keydown(event) ⇒ boolean

Handle the indicated keyboard event.

The default implementation of this method does nothing. This will typically be handled by other mixins.

Kind: instance method of Carousel. Defined by Keyboard mixin. Returns: boolean - true if the event was handled

| Param | Type | Description | | --- | --- | --- | | event | KeyboardEvent | the keyboard event |

carousel.navigationAxis : string

Indicates the direction of permitted navigation with the keyboard.

Accepted values are "horizontal", "vertical", or "both" (the default). If this property is "horizontal", the Up Arrow and Down Arrow keys will be ignored. Conversely, if this is "vertical", the Left Arrow and Right Arrow keys will be ignored.

Kind: instance property of Carousel. Defined by KeyboardDirection mixin.

"selected-index-changed"

Fires when the selectedIndex property changes.

Kind: event emitted by Carousel. Defined by ItemsSelection mixin.

| Param | Type | Description | | --- | --- | --- | | detail.selectedIndex | number | The new selected index. |

"selected-item-changed"

Fires when the selectedItem property changes.

Kind: event emitted by Carousel. Defined by ItemsSelection mixin.

| Param | Type | Description | | --- | --- | --- | | detail.selectedItem | HTMLElement | The new selected item. | | detail.previousItem | HTMLElement | The previously selected item. |

carousel.selectedFraction : number

A fractional value indicating how far the user has currently advanced to the next/previous item. E.g., a selectedFraction of 3.5 indicates the user is halfway between items 3 and 4.

For more details, see the FractionalSelection mixin.

Kind: instance property of Carousel. Defined by SelectionAnimation mixin.

carousel.selectedFraction : number

A fractional value indicating how far the user has currently advanced to the next/previous item. E.g., a selectedFraction of 3.5 indicates the user is halfway between items 3 and 4.

Kind: instance property of Carousel. Defined by FractionalSelection mixin.

carousel.selectedIndex : number

The index of the item which is currently selected.

If selectionWraps is false, the index is -1 if there is no selection. In that case, setting the index to -1 will deselect any currently-selected item.

Kind: instance property of Carousel. Defined by ItemsSelection mixin.

carousel.selectedItem : object

The currently selected item, or null if there is no selection.

Setting this property to null deselects any currently-selected item.

Kind: instance property of Carousel. Defined by ItemsSelection mixin.

carousel.selectedItem : HTMLElement

The currently selected item, or null if there is no selection.

Kind: instance property of Carousel. Defined by TargetSelection mixin.

carousel.selectFirst()

Select the first item in the list.

Kind: instance method of Carousel. Defined by ItemsSelection mixin.

carousel.selectionAnimationDuration : number

The duration of a selection animation in milliseconds.

This measures the amount of time required for a selection animation to complete. This number remains constant, even if the number of items being animated increases.

The default value is 250 milliseconds (a quarter a second).

Kind: instance property of Carousel. Defined by SelectionAnimation mixin. Default: 250

carousel.selectionAnimationEffect : string

The name of a standard selection animation effect.

This is a shorthand for setting the selectionAnimationKeyframes property to standard keyframes. Supported string values:

• "crossfade"

• "reveal"

• "revealWithFade"

• "showAdjacent"

• "slide"

• "slideWithGap"

  Kind: instance property of Carousel. Defined by SelectionAnimation mixin. Default: "&quot;slide&quot;"
  

carousel.selectionAnimationKeyframes : Array.<cssRules>

The keyframes that define an animation that plays for an item when moving forward in the sequence.

This is an array of CSS rules that will be applied. These are used as keyframes to animate the item with the Web Animations API.

The animation represents the state of the next item as it moves from completely unselected (offstage, usually right), to selected (center stage), to completely unselected (offstage, usually left). The center time of the animation should correspond to the item's quiscent selected state, typically in the center of the stage and at the item's largest size.

The default forward animation is a smooth slide at full size from right to left.

When moving the selection backward, this animation is played in reverse.

Kind: instance property of Carousel. Defined by SelectionAnimation mixin.

carousel.selectionRequired : boolean

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

Kind: instance property of Carousel. Defined by ItemsSelection mixin. Default: false

carousel.selectionWraps : boolean

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

Kind: instance property of Carousel. Defined by ItemsSelection mixin. Default: false

carousel.selectionWraps : boolean

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

Kind: instance property of Carousel. Defined by TargetSelection mixin. Default: {false}

carousel.selectLast()

Select the last item in the list.

Kind: instance method of Carousel. Defined by ItemsSelection mixin.

carousel.selectNext()

Select the next item in the list.

Kind: instance method of Carousel. Defined by ItemsSelection mixin.

carousel.selectPrevious()

Select the previous item in the list.

Kind: instance method of Carousel. Defined by ItemsSelection mixin.

carousel.showTransition : boolean

Determine whether a transition should be shown during selection.

Components like carousels often define animated CSS transitions for sliding effects. Such a transition should usually not be applied while the user is dragging, because a CSS animation will introduce a lag that makes the swipe feel sluggish. Instead, as long as the user is dragging with their finger down, the transition should be suppressed. When the user releases their finger, the transition can be restored, allowing the animation to show the carousel sliding into its final position.

Note: This property is only intended to let a component cooperate with mixins that may be applied to it, and is not intended to let someone using component permanently enable or disable transition effects.

Kind: instance property of Carousel. Defined by SelectionAnimation mixin.

carousel.target : HTMLElement

Gets/sets the target element to which this component will delegate selection actions.

Kind: instance property of Carousel. Defined by TargetSelection mixin.

carousel.target : HTMLElement

Gets/sets the current target of the component.

Set this to point to another element. That target element will be implicitly added to the component's collective. That is, the component and its target will share responsibility for handling keyboard events.

You can set this property yourself, or you can use the ContentFirstChildTarget mixin to automatically set the target to the component's first child.

Kind: instance property of Carousel. Defined by TargetInCollective mixin.

carousel.travelFraction : number

The distance the first touchpoint has traveled since the beginning of a drag, expressed as a fraction of the element's width.

Kind: instance property of Carousel. Defined by SwipeDirection mixin.

carousel.travelFraction : number

The distance the user has moved the first touchpoint since the beginning of a trackpad/wheel operation, expressed as a fraction of the element's width.

Kind: instance property of Carousel. Defined by TrackpadDirection mixin.