# Class: Dropdown

## LuCI.ui. Dropdown

The `Dropdown` class implements a rich, stylable dropdown menu which supports non-text choice labels.

UI widget instances are usually not supposed to be created by view code directly, instead they're implicitely created by `LuCI.form` when instantiating CBI forms.

This class is automatically instantiated as part of `LuCI.ui`. To use it in views, use `'require ui'` and refer to `ui.Dropdown`. To import it in external JavaScript, use `L.require("ui").then(...)` and access the `Dropdown` property of the class instance value.

#### new LuCI.ui.Dropdown(value, choices, options)

ui.js, line 862

  Instantiate a rich dropdown choice widget.

  Name | Type | Default | Description
  --- | --- | --- | ---
  `value` | string | Array.<string> | null | optional The initial input value(s).
  `choices` | Object.<string, *> |  | Object containing the selectable choices of the widget. The object keys serve as values for the different choices while the values are used as choice labels.
  `options` | LuCI.ui.Dropdown.InitOptions |  | optional Object describing the widget specific options to initialize the dropdown.

### Extends

- LuCI.ui.AbstractElement

### Methods

#### addChoices(values, labels)

ui.js, line 1663

  Add new choices to the dropdown menu.

  This function adds further choices to an existing dropdown menu, ignoring choice values which are already present.

  Name | Type | Description
  --- | --- | ---
  `values` | Array.<string> | The choice values to add to the dropdown widget.
  `labels` | Object.<string, *> | The choice label values to use when adding dropdown choices. If no label is found for a particular choice value, the value itself is used as label text. Choice labels may be any valid value accepted by `LuCI.dom#content`.

#### clearChoices(reset_value)

ui.js, line 1628

  Remove all existing choices from the dropdown menu.

  This function removes all preexisting dropdown choices from the widget, keeping only choices currently being selected unless `reset_values` is given, in which case all choices and deselected and removed.

  Name | Type | Default | Description
  --- | --- | --- | ---
  `reset_value` | boolean | false | optional If set to `true`, deselect and remove selected choices as well instead of keeping them.

#### closeAllDropdowns()

ui.js, line 1696

  Close all open dropdown widgets in the current document.

#### inherited getValue(){string|Array.<string>|null}

ui.js, line 1905

  Read the current value of the input widget.

  ##### Returns:

  Type | Description
  --- | ---
  string | Array.<string> | null | The current value of the input element. For simple inputs like text fields or selects, the return value type will be a - possibly empty - string. Complex widgets such as `DynamicList` instances may result in an array of strings or `null` for unset values.

#### inherited isChanged(){boolean}

ui.js, line 141

  Check whether the input value was altered by the user.

  ##### Returns:

  Type | Description
  --- | ---
  boolean | Returns `true` if the input value has been altered by the user or `false` if it is unchaged. Note that if the user modifies the initial value and changes it back to the original state, it is still reported as changed.

#### inherited isValid(){boolean}

ui.js, line 154

  Check whether the current input value is valid.

  ##### Returns:

  Type | Description
  --- | ---
  boolean | Returns `true` if the current input value is valid or `false` if it does not meet the validation constraints.

#### inherited registerEvents(targetNode, synevent, events)

ui.js, line 203

  Dispatch a custom (synthetic) event in response to received events.

  Sets up event handlers on the given target DOM node for the given event names that dispatch a custom event of the given type to the widget root DOM node.

  The primary purpose of this function is to set up a series of custom uniform standard events such as `widget-update`, `validation-success`, `validation-failure` etc. which are triggered by various different widget specific native DOM events.

  Name | Type | Description
  --- | --- | ---
  `targetNode` | Node | Specifies the DOM node on which the native event listeners should be registered.
  `synevent` | string | The name of the custom event to dispatch to the widget root DOM node.
  `events` | Array.<string> | The native DOM events for which event handlers should be registered.

#### inherited render(){Node}

ui.js, line 1016

  Render the widget, setup event listeners and return resulting markup.

  ##### Returns:

  Type | Description
  --- | ---
  Node | Returns a DOM Node or DocumentFragment containing the rendered widget markup.

#### inherited setChangeEvents(targetNode, events)

ui.js, line 271

  Setup listeners for native DOM events that may change the widget value.

  Sets up event handlers on the given target DOM node for the given event names which may cause the input value to change completely, such as `change` events in a select menu. In contrast to update events, such change events will not trigger input value validation but they may cause field dependencies to get re-evaluated and will mark the input widget as dirty.

  Name | Type | Description
  --- | --- | ---
  `targetNode` | Node | Specifies the DOM node on which the event listeners should be registered.
  `events` | string | repeatable The DOM events for which event handlers should be registered.

#### inherited setPlaceholder(value)

ui.js, line 113

  Set the current placeholder value of the input widget.

  Name | Type | Description
  --- | --- | ---
  `value` | string | Array.<string> | null | The placeholder to set for the input element. Only applicable to text inputs, not to radio buttons, selects or similar.

#### inherited setUpdateEvents(targetNode, events)

ui.js, line 228

  Setup listeners for native DOM events that may update the widget value.

  Sets up event handlers on the given target DOM node for the given event names which may cause the input value to update, such as `keyup` or `onclick` events. In contrast to change events, such update events will trigger input value validation.

  Name | Type | Description
  --- | --- | ---
  `targetNode` | Node | Specifies the DOM node on which the event listeners should be registered.
  `events` | string | repeatable The DOM events for which event handlers should be registered.

#### inherited setValue(value)

ui.js, line 1878

  Set the current value of the input widget.

  Name | Type | Description
  --- | --- | ---
  `value` | string | Array.<string> | null | The value to set the input element to. For simple inputs like text fields or selects, the value should be a - possibly empty - string. Complex widgets such as `DynamicList` instances may accept string array or `null` values.

#### inherited triggerValidation()

ui.js, line 168

  Force validation of the current input value.

  Usually input validation is automatically triggered by various DOM events bound to the input widget. In some cases it is required though to manually trigger validation runs, e.g. when programmatically altering values.

### Type Definitions

#### LuCI.ui.Dropdown.InitOptionsLuCI.ui.AbstractElement.InitOptions

  In addition to the `AbstractElement.InitOptions` the following properties are recognized:

  ##### Properties:

  Name | Type | Argument | Default | Description
  --- | --- | --- | --- | ---
  `optional` | boolean | <optional> | true | Specifies whether the dropdown selection is optional. In contrast to other widgets, the `optional` constraint of dropdowns works differently; instead of marking the widget invalid on empty values when set to `false`, the user is not allowed to deselect all choices. For single value dropdowns that means that no empty "please select" choice is offered and for multi value dropdowns, the last selected choice may not be deselected without selecting another choice first.
  `multiple` | boolean | <optional> |  | Specifies whether multiple choice values may be selected. It defaults to `true` when an array is passed as input value to the constructor.
  `sort` | boolean | Array.<string> | <optional> | false | Specifies if and how to sort choice values. If set to `true`, the choice values will be sorted alphabetically. If set to an array of strings, the choice sort order is derived from the array.
  `select_placeholder` | string | <optional> | -- Please choose -- | Specifies a placeholder text which is displayed when no choice is selected yet.
  `custom_placeholder` | string | <optional> | -- custom -- | Specifies a placeholder text which is displayed in the text input field allowing to enter custom choice values. Only applicable if the `create` option is set to `true`.
  `create` | boolean | <optional> | false | Specifies whether custom choices may be entered into the dropdown widget.
  `create_query` | string | <optional> | .create-item-input | Specifies a CSS selector expression used to find the input element which is used to enter custom choice values. This should not normally be used except by widgets derived from the Dropdown class.
  `create_template` | string | <optional> | script[type="item-template"] | Specifies a CSS selector expression used to find an HTML element serving as template for newly added custom choice values. Any `{{value}}` placeholder string within the template elements text content will be replaced by the user supplied choice value, the resulting string is parsed as HTML and appended to the end of the choice list. The template markup may specify one HTML element with a `data-label-placeholder` attribute which is replaced by a matching label value from the `choices` object or with the user supplied value itself in case `choices` contains no matching choice label. If the template element is not found or if no `create_template` selector expression is specified, the default markup for newly created elements is `<li data-value="{{value}}"><span data-label-placeholder="true" /></li>`.
  `create_markup` | string | <optional> |  | This property allows specifying the markup for custom choices directly instead of referring to a template element through CSS selectors. Apart from that it works exactly like `create_template`.
  `display_items` | number | <optional> | 3 | Specifies the maximum amount of choice labels that should be shown in collapsed dropdown state before further selected choices are cut off. Only applicable when `multiple` is `true`.
  `dropdown_items` | number | <optional> | -1 | Specifies the maximum amount of choices that should be shown when the dropdown is open. If the amount of available choices exceeds this number, the dropdown area must be scrolled to reach further items. If set to `-1`, the dropdown menu will attempt to show all choice values and only resort to scrolling if the amount of choices exceeds the available screen space above and below the dropdown widget.
  `placeholder` | string | <optional> |  | This property serves as a shortcut to set both `select_placeholder` and `custom_placeholder`. Either of these properties will fallback to `placeholder` if not specified.
  `readonly` | boolean | <optional> | false | Specifies whether the custom choice input field should be rendered readonly. Only applicable when `create` is `true`.
  `maxlength` | number | <optional> |  | Specifies the HTML `maxlength` attribute to set on the custom choice `<input>` element. Note that this a legacy property that exists for compatibility reasons. It is usually better to `maxlength(N)` validation expression. Only applicable when `create` is `true`.