--- title: ComboBox description: ComboBox element: vaadin-combo-box --- ## Description `` is a web component for choosing a value from a filterable list of options presented in a dropdown overlay. The options can be provided as a list of strings or objects by setting [`items`](/elements/vaadin-combo-box#items) property on the element. ```html ``` ```js document.querySelector('#combo-box').items = ['apple', 'orange', 'banana']; ``` When the selected `value` is changed, a `value-changed` event is triggered. ### Item rendering To customize the content of the `` elements placed in the dropdown, use [`renderer`](/elements/vaadin-combo-box#renderer) property which accepts a function. The renderer function is called with `root`, `comboBox`, and `model` as arguments. Generate DOM content by using `model` object properties if needed, and append it to the `root` element. The `comboBox` reference is provided to access the combo-box element state. Do not set combo-box properties in a `renderer` function. ```js const comboBox = document.querySelector('#combo-box'); comboBox.items = [{'label': 'Hydrogen', 'value': 'H'}]; comboBox.renderer = (root, comboBox, model) => { const item = model.item; root.innerHTML = `${model.index}: ${item.label} ${item.value}`; }; ``` Renderer is called on the opening of the combo-box and each time the related model is updated. Before creating new content, it is recommended to check if there is already an existing DOM element in `root` from a previous renderer call for reusing it. Even though combo-box uses infinite scrolling, reducing DOM operations might improve performance. The following properties are available in the `model` argument: Property | Type | Description -----------|------------------|------------- `index` | Number | Index of the item in the `items` array `item` | String or Object | The item reference `selected` | Boolean | True when item is selected `focused` | Boolean | True when item is focused ### Lazy Loading with Function Data Provider In addition to assigning an array to the items property, you can alternatively use the [`dataProvider`](/elements/vaadin-combo-box#dataprovider) function property. The `` calls this function lazily, only when it needs more data to be displayed. __Note that when using function data providers, the total number of items needs to be set manually. The total number of items can be returned in the second argument of the data provider callback:__ ```js comboBox.dataProvider = async (params, callback) => { const API = 'https://demo.vaadin.com/demo-data/1.0/filtered-countries'; const { filter, page, pageSize } = params; const index = page * pageSize; const res = await fetch(`${API}?index=${index}&count=${pageSize}&filter=${filter}`); if (res.ok) { const { result, size } = await res.json(); callback(result, size); } }; ``` ### Styling The following custom properties are available for styling: Custom property | Description | Default ----------------------------------------|----------------------------|--------- `--vaadin-field-default-width` | Default width of the field | `12em` `--vaadin-combo-box-overlay-width` | Width of the overlay | `auto` `--vaadin-combo-box-overlay-max-height` | Max height of the overlay | `65vh` The following shadow DOM parts are available for styling: Part name | Description ---------------------|---------------- `label` | The label element `input-field` | The element that wraps prefix, value and buttons `field-button` | Set on both clear and toggle buttons `clear-button` | The clear button `error-message` | The error message element `helper-text` | The helper text element wrapper `required-indicator` | The `required` state indicator element `toggle-button` | The toggle button `overlay` | The overlay container `content` | The overlay content `loader` | The loading indicator shown while loading items The following state attributes are available for styling: Attribute | Description ---------------------|--------------------------------- `disabled` | Set when the element is disabled `has-value` | Set when the element has a value `has-label` | Set when the element has a label `has-helper` | Set when the element has helper text or slot `has-error-message` | Set when the element has an error message `has-tooltip` | Set when the element has a slotted tooltip `invalid` | Set when the element is invalid `focused` | Set when the element is focused `focus-ring` | Set when the element is keyboard focused `readonly` | Set when the element is readonly `opened` | Set when the overlay is opened `loading` | Set when loading items from the data provider ### Internal components In addition to `` itself, the following internal components are themable: - `` - has the same API as [``](/elements/vaadin-item). See [Styling Components](https://vaadin.com/docs/latest/styling/styling-components) documentation. ## Properties ### accessibleName **Type:** `string | null | undefined` String used to label the component to screen reader users. ### accessibleNameRef **Type:** `string | null | undefined` Id of the element used as label of the component to screen reader users. ### allowCustomValue **Type:** `boolean` If `true`, the user can input a value that is not present in the items list. `value` property will be set to the input value in this case. Also, when `value` is set programmatically, the input value will be set to reflect that value. ### allowedCharPattern **Type:** `string` A pattern matched against individual characters the user inputs. When set, the field will prevent: - `keydown` events if the entered key doesn't match `/^allowedCharPattern$/` - `paste` events if the pasted text doesn't match `/^allowedCharPattern*$/` - `drop` events if the dropped text doesn't match `/^allowedCharPattern*$/` For example, to allow entering only numbers and minus signs, use: `allowedCharPattern = "[\\d-]"` ### autofocus **Type:** `boolean` Specify that this control should have input focus when the page loads. ### autoOpenDisabled **Type:** `boolean | null | undefined` Set true to prevent the overlay from opening automatically. ### autoselect **Type:** `boolean` If true, the input text gets fully selected when the field is focused using click or touch / tap. ### clearButtonVisible **Type:** `boolean` Set to true to display the clear icon which clears the input. It is up to the component to choose where to place the clear icon: in the Shadow DOM or in the light DOM. In any way, a reference to the clear icon element should be provided via the `clearElement` getter. ### dataProvider **Type:** `ComboBoxDataProvider | null | undefined` Function that provides items lazily. Receives arguments `params`, `callback` `params.page` Requested page index `params.pageSize` Current page size `params.filter` Currently applied filter `callback(items, size)` Callback function with arguments: - `items` Current page of items - `size` Total number of items. See also: [ComboBoxDataProvider](#comboboxdataprovider) ### disabled **Type:** `boolean` If true, the user cannot interact with this element. ### errorMessage **Type:** `string | null | undefined` Error to show when the field is invalid. ### filter **Type:** `string` Filtering string the user has typed into the input field. ### filteredItems **Type:** `any[] | undefined` A subset of items, filtered based on the user input. Filtered items can be assigned directly to omit the internal filtering functionality. The items can be of either `String` or `Object` type. ### helperText **Type:** `string | null | undefined` String used for the helper text. ### invalid **Type:** `boolean` Set to true when the field is invalid. ### itemClassNameGenerator **Type:** `(item: any) => string` A function used to generate CSS class names for dropdown items based on the item. The return value should be the generated class name as a string, or multiple class names separated by whitespace characters. ### itemIdPath **Type:** `string | null | undefined` Path for the id of the item. If `items` is an array of objects, the `itemIdPath` is used to compare and identify the same item in `selectedItem` and `filteredItems` (items given by the `dataProvider` callback). ### itemLabelGenerator **Type:** `((item: any) => string) | undefined` A function that is used to generate the label for dropdown items based on the item. Receives one argument: - `item` The item to generate the label for. ### itemLabelPath **Type:** `string` Path for label of the item. If `items` is an array of objects, the `itemLabelPath` is used to fetch the displayed string label for each item. The item label is also used for matching items when processing user input, i.e., for filtering and selecting items. ### items **Type:** `any[] | undefined` A full set of items to filter the visible options from. The items can be of either `String` or `Object` type. ### itemValuePath **Type:** `string` Path for the value of the item. If `items` is an array of objects, the `itemValuePath:` is used to fetch the string value for the selected item. The item value is used in the `value` property of the combo box, to provide the form value. ### label **Type:** `string | null | undefined` The label text for the input node. When no light dom defined via [slot=label], this value will be used. ### loading **Type:** `boolean` When set to `true`, "loading" attribute is added to host and the overlay element. ### manualValidation **Type:** `boolean` Set to true to enable manual validation mode. This mode disables automatic constraint validation, allowing you to control the validation process yourself. You can still trigger constraint validation manually with the `validate()` method or use `checkValidity()` to assess the component's validity without affecting the invalid state. In manual validation mode, you can also manipulate the `invalid` property directly through your application logic without conflicts with the component's internal validation. ### name **Type:** `string` The name of this field. ### opened **Type:** `boolean` True if the dropdown is open, false otherwise. ### pageSize **Type:** `number` Number of items fetched at a time from the dataprovider. ### pattern **Type:** `string` A regular expression that the value is checked against. The pattern must match the entire value, not just some subset. ### placeholder **Type:** `string` A hint to the user of what can be entered in the field. ### readonly **Type:** `boolean` When present, it specifies that the field is read-only. ### renderer **Type:** `ComboBoxRenderer | null | undefined` Custom function for rendering the content of every item. Receives three arguments: - `root` The `` internal container DOM element. - `comboBox` The reference to the `` element. - `model` The object with the properties related with the rendered item, contains: - `model.index` The index of the rendered item. - `model.item` The item. See also: [ComboBoxRenderer](#comboboxrenderer) ### required **Type:** `boolean` Specifies that the user must fill in a value. ### selectedItem **Type:** `any` The selected item from the `items` array. ### size **Type:** `number | undefined` Total number of items. ### title **Type:** `string` The text usually displayed in a tooltip popup when the mouse is over the field. ### value **Type:** `string` The value of the field. ## Methods ### cancel **Type:** `any` Reverts back to original value. ### checkValidity **Type:** `() => boolean` Returns true if the field value satisfies all constraints (if any). ### clear **Type:** `() => void` Clear the value of the field. ### clearCache **Type:** `() => void` Clears the cached pages and reloads data from dataprovider when needed. ### close **Type:** `() => void` Closes the dropdown list. ### open **Type:** `() => void` Opens the dropdown list. ### requestContentUpdate **Type:** `() => void` Requests an update for the content of items. While performing the update, it invokes the renderer (passed in the `renderer` property) once an item. It is not guaranteed that the update happens immediately (synchronously) after it is requested. ### validate **Type:** `() => boolean` Validates the field and sets the `invalid` property based on the result. The method fires a `validated` event with the result of the validation. ## Events ### change **Type:** [ComboBoxChangeEvent](#comboboxchangeevent) Fired when the user commits a value change. ### custom-value-set **Type:** [ComboBoxCustomValueSetEvent](#comboboxcustomvaluesetevent) Fired when the user sets a custom value. ### filter-changed **Type:** [ComboBoxFilterChangedEvent](#comboboxfilterchangedevent) Fired when the `filter` property changes. ### input **Type:** `CustomEvent` Fired when the value is changed by the user: on every typing keystroke, and the value is cleared using the clear button. ### invalid-changed **Type:** [ComboBoxInvalidChangedEvent](#comboboxinvalidchangedevent) Fired when the `invalid` property changes. ### opened-changed **Type:** [ComboBoxOpenedChangedEvent](#comboboxopenedchangedevent) Fired when the `opened` property changes. ### selected-item-changed **Type:** [ComboBoxSelectedItemChangedEvent](#comboboxselecteditemchangedevent) Fired when selected item changes. ### vaadin-combo-box-dropdown-closed **Type:** `CustomEvent` Fired after the `vaadin-combo-box-overlay` closes. ### vaadin-combo-box-dropdown-opened **Type:** `CustomEvent` Fired after the `vaadin-combo-box-overlay` opens. ### validated **Type:** [ComboBoxValidatedEvent](#comboboxvalidatedevent) Fired whenever the field is validated. ### value-changed **Type:** [ComboBoxValueChangedEvent](#comboboxvaluechangedevent) Fired when the value changes. ## Types ### ComboBoxChangeEvent ```ts /** * Fired when the user commits a value change. */ export type ComboBoxChangeEvent = Event & { target: ComboBox; }; ``` ### ComboBoxCustomValueSetEvent ```ts /** * Fired when the user sets a custom value. */ export type ComboBoxCustomValueSetEvent = CustomEvent; ``` ### ComboBoxDataProvider ```ts export type ComboBoxDataProvider = ( params: ComboBoxDataProviderParams, callback: ComboBoxDataProviderCallback, ) => void; ``` ### ComboBoxDataProviderCallback ```ts export type ComboBoxDataProviderCallback = (items: TItem[], size?: number) => void; ``` ### ComboBoxDataProviderParams ```ts export interface ComboBoxDataProviderParams { page: number; pageSize: number; filter: string; } ``` ### ComboBoxFilterChangedEvent ```ts /** * Fired when the `filter` property changes. */ export type ComboBoxFilterChangedEvent = CustomEvent<{ value: string }>; ``` ### ComboBoxInvalidChangedEvent ```ts /** * Fired when the `invalid` property changes. */ export type ComboBoxInvalidChangedEvent = CustomEvent<{ value: boolean }>; ``` ### ComboBoxItemModel ```ts export interface ComboBoxItemModel { index: number; item: TItem; selected: boolean; focused: boolean; } ``` ### ComboBoxItemRenderer ```ts export type ComboBoxItemRenderer = ( root: HTMLElement, owner: TOwner, model: ComboBoxItemModel, ) => void; ``` ### ComboBoxOpenedChangedEvent ```ts /** * Fired when the `opened` property changes. */ export type ComboBoxOpenedChangedEvent = CustomEvent<{ value: boolean }>; ``` ### ComboBoxRenderer ```ts export type ComboBoxRenderer = ComboBoxItemRenderer>; ``` ### ComboBoxSelectedItemChangedEvent ```ts /** * Fired when the `selectedItem` property changes. */ export type ComboBoxSelectedItemChangedEvent = CustomEvent<{ value: TItem | null | undefined }>; ``` ### ComboBoxValidatedEvent ```ts /** * Fired whenever the field is validated. */ export type ComboBoxValidatedEvent = CustomEvent<{ valid: boolean }>; ``` ### ComboBoxValueChangedEvent ```ts /** * Fired when the `value` property changes. */ export type ComboBoxValueChangedEvent = CustomEvent<{ value: string }>; ```