DropdownList

Shows a single choice made from a pop-up list of choices
Beginner Intermediate Expert
Demo: The user can click the current choice to change it

Overview

This component shows a single choice made from a pop-up list of choices. This it shows a clone of the currently-selected item as the button label.

Generally speaking, DropdownList serves as a customizable form of the standard select element. By permitting any type of content as list items, you can customize the presentation of the choices and current value beyond what's possible in a select:

Black Blue Green Orange Purple Red White Yellow
Demo: DropdownList showing custom elements as choices

Usage

import DropdownList from "elix/define/DropdownList.js";
const dropdownList = new DropdownList(); // or
const dropdownList = document.createElement("elix-dropdown-list");

In HTML:

<script type="module" src="node_modules/elix/define/DropdownList.js"></script>
<elix-dropdown-list aria-label="Skill level">
  <div>Beginner</div>
  <div>Intermediate</div>
  <div>Expert</div>
</elix-dropdown-list>

Use DropdownList when:

  • The set of choices is fairly small.
  • Space is limited, or you don't need to draw much attention to the setting controlled by the list. If you have sufficient room, an in situ ListBox may let the user make a selection more quickly and easily.

See also

MenuButton
A button that invokes a menu
ListBox
Single-selection list box
ListComboBox
A combo box whose popup presents a list of choices
SpinBox
Input with buttons to increase or decrease a value

API

Class hierarchy:

The element defines the following shadow parts:

  • down-icon: the icon shown in the toggle if the popup will open or close in the down direction
  • list: the list shown in the popup, default type is div element
  • popup: the popup element, default type is Popup
  • popup-toggle: the element that lets the user know they can open the popup, default type is UpDownToggle
  • source: the element used as the reference point for positioning the popup, generally the element that invokes the popup, default type is button element
  • up-icon: the icon shown in the toggle if the popup will open or close in the up direction
  • value: region inside the toggle button showing the value of the current selection, default type is div element

close(closeResult) method

Close the component (if not already closed).

Some components like AlertDialog want to indicate why or how they were closed. To support such scenarios, you can supply a value to the optional closeResult parameter. This closeResult will be made available in the whenClosed promise and the state.closeResult member.

Parameters:

  • closeResult: objectan indication of how or why the element closed

Defined by OpenCloseMixin

close event

Raised when the component closes.

Defined by OpenCloseMixin

closed property

True if the element is currently closed.

This read-only property is provided as a convenient inverse of opened.

Type: boolean

Defined by OpenCloseMixin

closeFinished property

True if the element has completely closed.

For components not using asynchronous open/close effects, this property returns the same value as the closed property. For elements that have a true value of state.openCloseEffects (e.g., elements using TransitionEffectMixin), this property returns true only if state.effect is "close" and state.effectPhase is "after".

Type: boolean

Defined by OpenCloseMixin

closestAvailableItemIndex(state, options) method

Look for an item which is available in the given state..

The options parameter can accept options for:

  • direction: 1 to move forward, -1 to move backward
  • index: the index to start at, defaults to state.currentIndex
  • wrap: whether to wrap around the ends of the items array, defaults to state.cursorOperationsWrap.

If an available item was found, this returns its index. If no item was found, this returns -1.

Parameters:

  • state: PlainObject
  • options: PlainObject

Returns: number

Defined by ItemsCursorMixin

contentSlot property

See contentSlot.

Defined by SlotContentMixin

currentIndex property

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

Type: number

Defined by CursorAPIMixin

currentindexchanged event

Raised when the currentIndex property changes.

Defined by CursorAPIMixin

currentItem property

The current item, or null if no item is current.

Type: Element

Defined by CursorAPIMixin

currentItemRequired property

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

Type: boolean

Default: false

Defined by CursorAPIMixin

cursorOperationsWrap property

True if cursor operations wrap from last to first, and vice versa.

Type: boolean

Default: false

Defined by CursorAPIMixin

defaultState property

The default state for the component. This can be extended by mixins and classes to provide additional default state.

Type: PlainObject

Defined by ReactiveMixin

delegatesFocus property

Returns true if the component is delegating its focus.

A component using DelegateFocusMixin will always have this property be true unless a class takes measures to override it.

Type: boolean

Default: true

Defined by DelegateFocusMixin

disabled property

True if the component is disabled, false (the default) if not.

The value of this property will be reflected to the disabled attribute so that it can be referenced in CSS. Note that this non-native implementation of the disabled attribute will not trigger the :disabled CSS pseudo-class, so your style rules will have to reference the presence or absence of the disabled attribute. That is, instead of writing

my-component:disabled { ... }

write this instead

my-component[disabled] { ... }

Like the native disabled attribute, this attribute is boolean. That means that it's existence in markup sets the attribute, even if set to an empty string or a string like "false".

Type: boolean

Default: false

Defined by DisabledMixin

disabledchange event

Raised when the disabled property changes.

Defined by DisabledMixin

form property

The ID of the form element with which this element is associated, or null if the element is not associated with any form. This is provided for consistency with the native HTML form property.

Type: string

Defined by FormElementMixin

getItemText(item) method

Extract the text from the given item.

The default implementation returns an item's aria-label, alt attribute, innerText, or textContent, in that order. You can override this to return the text that should be used.

Parameters:

  • item: Element

Returns: string

Defined by SelectedTextAPIMixin

goFirst() method

Moves to the first item in the list.

Returns: Boolean True if the current item changed, false if not.

Defined by CursorAPIMixin

goLast() method

Move to the last item in the list.

Returns: Boolean True if the current item changed

Defined by CursorAPIMixin

goNext() method

Move to the next item in the list.

If the list has no current item, the first item will become current.

Returns: Boolean True if the current item changed

Defined by CursorAPIMixin

goPrevious() method

Moves to the previous item in the list.

If the list has no current item, the last item will become current.

Returns: Boolean True if the current item changed

Defined by CursorAPIMixin

horizontalAlign property

The alignment of the popup with respect to the source button.

  • start: popup and source are aligned on the leading edge according to the text direction
  • end: popup and source are aligned on the trailing edge according to the text direction
  • left: popup and source are left-aligned
  • right: popup and source are right-aligned
  • `stretch: both left and right edges are aligned
     <p><span class="apiLabel">Type:</span> <code>'start'|'end'|'left'|'right'|'stretch'</code></p> <p><span class="apiLabel">Default:</span> <code>'start'</code></p>  <p> Defined by <a href="PopupSource">PopupSource</a> </p> 

ids 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[ids].foo to obtain the corresponding button in the component instance's shadow tree. The ids property is simply a shorthand for getElementById, so this[ids].foo is the same as this[shadowRoot].getElementById('foo').

Type: object

Defined by ShadowTemplateMixin

[internal.goFirst]() method

Move to the first item in the set.

Returns: Boolean True if the current item changed, false if not.

Defined by ItemsCursorMixin

[internal.goLast]() method

Move to the last item in the set.

Returns: Boolean True if the current item changed, false if not.

Defined by ItemsCursorMixin

[internal.goNext]() method

Move to the next item in the set.

If no item is current, move to the first item.

Returns: Boolean True if the current item changed, false if not.

Defined by ItemsCursorMixin

[internal.goPrevious]() method

Move to the previous item in the set.

If no item is current, move to the last item.

Returns: Boolean True if the current item changed, false if not.

Defined by ItemsCursorMixin

items property

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

Type: Array.

Defined by ItemsAPIMixin

itemschange event

Raised when the items property changes.

Defined by ItemsAPIMixin

keydown() method

See the symbols documentation for details.

Defined by KeyboardMixin

listPartType property

The class or tag used to define the list part – the element presenting the list items and handling navigation between them.

Type: (component class constructor)|HTMLTemplateElement|string

Default: List

name property

The name of the form field that will be filled with this element's value. This is an analogue of the standard HTML name property.

Type: string

Defined by FormElementMixin

open() method

Open the element (if not already opened).

Defined by OpenCloseMixin

open event

Raised when the component opens.

Defined by OpenCloseMixin

opened property

True if the element is currently opened.

This property can be set as a boolean attribute

Type: boolean

Default: false

Defined by OpenCloseMixin

openedchange event

Raised when the opened/closed state of the component changes.

Defined by OpenCloseMixin

popupPartType property

The class or tag used to create the popup part – the element responsible for displaying the popup and handling overlay behavior.

Type: (component class constructor)|HTMLTemplateElement|string

Default: Popup

Defined by PopupSource

popupPosition property

The preferred direction for the popup.

  • above: popup should appear above the source
  • below: popup should appear below the source
     <p><span class="apiLabel">Type:</span> <code>'above'|'below'</code></p> <p><span class="apiLabel">Default:</span> <code>'below'</code></p>  <p> Defined by <a href="PopupSource">PopupSource</a> </p> 

popupTogglePartType property

The class or tag used to create the popup-toggle part – the element that lets the user know they can open the popup.

Type: (component class constructor)|HTMLTemplateElement|string

Default: UpDownToggle

Defined by PopupToggleMixin

render(changed) method

Render the indicated changes in state to the DOM.

The default implementation of this method does nothing. Override this method in your component to update your component's host element and any shadow elements to reflect the component's new state. See the rendering example.

Be sure to call super in your method implementation so that your component's base classes and mixins have a chance to perform their own render work.

Parameters:

  • changed: ChangedFlagsdictionary of flags indicating which state members have changed since the last render

Defined by ReactiveMixin

renderChanges() method

Render any pending component changes to the DOM.

This method does nothing if the state has not changed since the last render call.

ReactiveMixin will invoke this method following a setState call; you should not need to invoke this method yourself.

This method invokes the internal render method, then invokes the rendered method.

Defined by ReactiveMixin

rendered(changed) method

Perform any work that must happen after state changes have been rendered to the DOM.

The default implementation of this method does nothing. Override this method in your component to perform work that requires the component to be fully rendered, such as setting focus on a shadow element or inspecting the computed style of an element. If such work should result in a change in component state, you can safely call setState during the rendered method.

Be sure to call super in your method implementation so that your component's base classes and mixins have a chance to perform their own post-render work.

Parameters:

  • changed: ChangedFlags

Defined by ReactiveMixin

selectCurrentItemAndClose() method

Highlight the current item (if one exists), then close the menu.

Defined by PopupListMixin

selectedIndex property

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

Type: number

Defined by SingleSelectAPIMixin

selectedindexchange event

Raised when the selectedIndex property changes.

Defined by SingleSelectAPIMixin

selectedItem property

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

Type: Element

Defined by SingleSelectAPIMixin

selectedText property

The text content of the selected item.

Setting this value to a string will attempt to select the first list item whose text matches that string. Setting this to a string not matching any list item will result in no selection.

Type: string

Defined by SelectedTextAPIMixin

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: PlainObjectthe changes to apply to the element's state

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

Defined by ReactiveMixin

sourcePartType property

The class or tag used to create the source part - the button (or other element) the user can tap/click to invoke the popup.

Type: (component class constructor)|HTMLTemplateElement|string

Default: 'button'

Defined by PopupSource

state property

The component's current state.

The returned state object is immutable. To update it, invoke internal.setState.

It's extremely useful to be able to inspect component state while debugging. If you append ?elixdebug=true to a page's URL, then ReactiveMixin will conditionally expose a public state property that returns the component's state. You can then access the state in your browser's debug console.

Type: PlainObject

Defined by ReactiveMixin

stateEffects(state, changed) method

Ask the component whether a state with a set of recently-changed fields implies that additional second-order changes should be applied to that state to make it consistent.

This method is invoked during a call to internal.setState to give all of a component's mixins and classes a chance to respond to changes in state. If one mixin/class updates state that it controls, another mixin/class may want to respond by updating some other state member that it controls.

This method should return a dictionary of changes that should be applied to the state. If the dictionary object is not empty, the internal.setState method will apply the changes to the state, and invoke this stateEffects method again to determine whether there are any third-order effects that should be applied. This process repeats until all mixins/classes report that they have no additional changes to make.

See an example of how ReactiveMixin invokes the stateEffects to ensure state consistency.

Parameters:

  • state: PlainObjecta proposal for a new state
  • changed: ChangedFlagsthe set of fields changed in this latest proposal for the new state

Returns: PlainObject

Defined by ReactiveMixin

toggle(opened) method

Toggle the open/close state of the element.

Parameters:

  • opened: booleantrue if the element should be opened, false if closed.

Defined by OpenCloseMixin

type property

The "type" of the form field, provided for consistency with the native HTML type property.

If a base class provides a type property, that will be returned. (If this mixin is applied to a class defined by WrappedStandardElement, this will return the type of the inner standard element.) Otherwise, the default value of this property will be the same as the HTML tag name registered for the custom element.

Type: string

Defined by FormElementMixin

value property

The text content of the selected item.

Setting this value to a string will attempt to select the first list item whose text content match that string. Setting this to a string not matching any list item will result in no selection.

Type: string

Defined by SelectedValueAPIMixin

valuePartType property

The class or tag used to create the value part - the region showing the dropdown list's current value.

Type: (component class constructor)|HTMLTemplateElement|string

Default: 'div'

whenClosed() method

This method can be used as an alternative to listening to the "openedchange" event, particularly in situations where you want to only handle the next time the component is closed.

Returns: Promise A promise that resolves when the element has completely closed, including the completion of any asynchronous opening effect.

Defined by OpenCloseMixin