Tabs

Overview

Tabs is a set of tabbed panels that can be navigated by selecting corresponding tab buttons. Tabs builds on Explorer, which takes care of the relative positioning of the tab buttons and the tab panels, and ensures that the selection state of the buttons and panels remains in sync. Tabs itself mostly adds the use of TabButton elements as default proxies for the tab panels (the elements the user can click to select a panel), and TabStrip to contain the list of tab buttons. Tabs also adds accessibility support specific to tabbed interfaces.

A typical example of Tabs being used for navigation, using custom tab buttons:

home
Home
search
Search
settings
Settings
Home page
Search page
Settings page
Demo: Tabs used for navigation

You can select a tab with mouse/touch or a keyboard.

The Tabs class is registered as element <elix-tabs>.

Usage

Use Tabs for situations in which the user can directly control which modal state is presented. Tabs are typically used to allow a UI to offer more controls than can fit in a confined area at a time.

  • A common use case is Settings or configuration UIs. Here the classic look of a tabbed dialog or property sheet is addressed with the Elix's default TabButton elements, although other looks are possible.
  • Tabs may also be used in a main window to downplay less-commonly used aspects of a UI.
  • Tabs are also an extremely common navigation model. Many mobile applications present a navigation toolbar that behave like tabs, presenting 3–5 buttons that correspond to the app's main areas. In navigation use cases, the tab buttons typically have a toolbar button style rather than a classic tabbed appearance.

Using default tab buttons

By default, you only need to provide Tabs with child items that it will use as the tab panels. For best results, give each panel a text lable in an aria-label attribute.

<elix-tabs>
  <div aria-label="One">Page one</div>
  <div aria-label="Two">Page two</div>
  <div aria-label="Three">Page three</div>
</elix-tabs>


For each panel, Tabs will create a TabButton instance, and that panel's aria-label as the content of the tab button.

Page one
Page two
Page three
Demo: Tabs element with default tab buttons

Positioning and aligning tab buttons

Tabs exposes proxyListPosition and tabAlign properties that let you control, respectively, how the strip of tabs is positioned with respect to the panels and how they are visually aligned within the strip of tabs.

Page one
Page two
Page three

Show tabs on:

Align tabs:

Demo: You can customize tab position and alignment

Custom content in default tab buttons

If you would like to use the default tab button appearance, but have more control over the content of the tab buttons, you can create the tab buttons yourself. Add a slot="tabButtons" attribute to each button to specify that you want it to be treated as a tab button:

<elix-tabs>
  <elix-tab-button slot="tabButtons">Un</elix-tab-button>
  <div aria-label="One">Page one</div>

  <elix-tab-button slot="tabButtons">Deux</elix-tab-button>
  <div aria-label="Two">Page two</div>

  <elix-tab-button slot="tabButtons">Trois</elix-tab-button>
  <div aria-label="Three">Page three</div>
</elix-tabs>


Because the <elix-tab-button> instances are HTML elements, you can include arbitrarily complex content inside them: add icons, other graphical elements, etc.

As long as the relative order of the tab buttons and the panel elements are consistent, it doesn't matter where the tab buttons appear. You can interleave them with the panels (above) or, if it's more convenient, group the tab buttons together:

<elix-tabs>
  <elix-tab-button slot="tabButtons">Un</elix-tab-button>
  <elix-tab-button slot="tabButtons">Trois</elix-tab-button>
  <elix-tab-button slot="tabButtons">Deux</elix-tab-button>

  <div aria-label="One">Page one</div>
  <div aria-label="Two">Page two</div>
  <div aria-label="Three">Page three</div>
</elix-tabs>


In either case, the result is:

Un Deux Trois
Page one
Page two
Page three
Demo: Tabs with custom content in standard tab buttons

Using custom tab buttons

You can also provide your custom elements as the tab buttons. For example, the demo showing tabs used for navigation at the top of this page can be created using code along these lines:

<elix-tabs tab-position="bottom" tab-align="stretch">

  <toolbar-tab slot="tabButtons" aria-label="Home">
    <div class="material-icons">home</div>
    Home
  </toolbar-tab>

  <toolbar-tab slot="tabButtons" aria-label="Search">
    <div class="material-icons">search</div>
    Search
  </toolbar-tab>

  <toolbar-tab slot="tabButtons" aria-label="Settings">
    <div class="material-icons">settings</div>
    Settings
  </toolbar-tab>

  <div>Home page</div>
  <div>Search page</div>
  <div>Settings page</div>

</elix-tabs>


This uses Google's Material Design icons for button icons, but you can use whatever techniques are appropriate for your app's visual design.

Customizing the stage

By default, Tabs uses Modes as the main stage showing the selected tab panel. Modes provides an immediate transition between panels, but you can override the stageTag property to specify another type of stage, such as CrossfadeStage:

Standard rooms

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Demo: CrossfadeStage provides a crossfade effect when switching tabs

The tabbed navigation example at the top of the page shows a SlidingPages element as the stage, which adds a horizontal sliding effect and support for touch/trackpad swipe gestures.

API

Ancestry: Tabs → ExplorerReactiveElement → HTMLElement

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

Includes subelements TabButton, TabStrip, and Modes.

$ 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

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 inherited from Explorer

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 inherited from Explorer

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

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 inherited from SlotItemsMixin

items property

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

Defined by ContentItemsMixin inherited from SlotItemsMixin

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 inherited from SlotItemsMixin

proxies property

The current set of proxy elements that correspond to the component's main items. If you have assigned elements to the proxy slot, this returns the collection of those elements. Otherwise, this will return a collection of default proxies generated by the component, one for each item.

Type: Array.

Inherited from Explorer

proxyListOverlap property

True if the list of proxies should overlap the stage, false if not.

Type: boolean

Default: {false}

Inherited from Explorer

proxyListPosition property

The position of the proxy list relative to the stage.

The start and end values refer to text direction: in left-to-right languages such as English, these are equivalent to left and right, respectively.

Type: 'bottom', 'end', 'left', 'right', 'start', 'top'

Default: 'start'

Inherited from Explorer

proxyListTag property

The tag used to create the Explorer's list of proxies.

Type: string

Default: 'div'

Inherited from Explorer

proxyTag property

The tag used to create default proxies for the list items.

Type: string

Default: 'div'

Inherited from Explorer

proxyUpdates(proxy, calcs) method

Determine what updates should be applied to a proxy to reflect the state of the corresponding item, 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 proxy during rendering.

The calcs parameter is an object with the following members:

  • index: the index of this proxy in the list.
  • isDefaultProxy: true if this proxy was generated by the Explorer, false if the proxy was assigned to the Explorer's proxy slot.
  • item: the list item corresponding to this proxy. E.g., for a tab button, the item is the corresponding tab panel.

Parameters:
  • proxy: Elementthe proxy to be updated
  • calcs: objectper-proxy calculations derived from element state

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

Inherited from Explorer

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 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

selected-index-changed event

Raised when the selectedIndex property changes.

Defined by SingleSelectionMixin inherited from Explorer

selectedIndex property

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

Type: number

Defined by SingleSelectionMixin inherited from Explorer

selectedItem property

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

Type: Element

Defined by SingleSelectionMixin inherited from Explorer

selectFirst() method

Select the first item in the list.

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

Defined by SingleSelectionMixin inherited from Explorer

selectionRequired property

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

Type: boolean

Default: false

Defined by SingleSelectionMixin inherited from Explorer

selectionWraps property

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

Type: boolean

Default: false

Defined by SingleSelectionMixin inherited from Explorer

selectLast() method

Select the last item in the list.

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

Defined by SingleSelectionMixin inherited from Explorer

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 inherited from Explorer

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 inherited from Explorer

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 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.

Parameters:
  • nextState: objectthe proposed new state for the element

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

Defined by ReactiveMixin inherited from ReactiveElement

stageTag property

The tag used to create the main "stage" element showing a single item at a time.

Type: string

Default: 'elix-modes'

Inherited from Explorer

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

tabAlign property

The alignment of the tabs within the tab strip.

The value of this property will be forwarded to the corresponding property

Type: 'start', 'center', 'end', 'stretch'

Default: 'start'

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