Text area that grows to accommodate its content
Type all you want here!
Demo: This text area grows as you add text


This text input component is useful in situations where you want to ask the user to enter as much text as they want, but don't want to take up a lot of room on the page.

Note: This component uses WrappedStandardElement to wrap a standard <textarea> element. This allows it to provide all standard HTMLTextAreaElement properties, methods, and events, in addition to those specifically listed in the AutoSizeTextarea API.


Ancestry: AutoSizeTextarea → WrappedStandardElementReactiveElement → HTMLElement

Built with mixins AttributeMarshallingMixin, ReactiveMixin, RenderUpdatesMixin, ShadowTemplateMixin, and SlotContentMixin.

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

Type: object

Defined by ShadowTemplateMixin

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

inner property

Returns a reference to the inner standard HTML element.

Type: Element

Defined by WrappedStandardElement

minimumRows property

Determines the minimum number of rows shown. This is similar to the rows attribute on a standard textarea, but because this element can grow, is expressed as a minimum rather than a fixed number.

By default, this property is 1, so when empty, the text area will be a single line tall. That's efficient in terms of the space it consumes, but until the user interacts with the element, they may not realize they can enter multiple lines of text. Setting the property to a value higher than 1 will signal to the user that they can enter multiple lines of a text.

By setting this property, you can also communicate to the user some sense of how much text you're expecting them to provide. For example, on a feedback form, asking the user to enter their feedback in a single-line text box implies you don't really want them to enter much text — even if the text box will grow when they type. By setting this to a value like, say, 10 rows, you can signal that you're fully expecting them to enter more text.

Type: number

Default: 1

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.


  • state: objecta proposed new state for the component

Returns: boolean - true if the state is already acceptable as it is

Defined by ReactiveMixin

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

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.


  • changes: objectthe changes to apply to the element's state

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

Defined by ReactiveMixin

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.


  • nextState: objectthe proposed new state for the element

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

Defined by ReactiveMixin

state property

The component's current state. The returned state object is immutable. To update it, invoke setState.

Type: object

Defined by ReactiveMixin

symbols.contentSlot property

Defined by SlotContentMixin

template property

The template copied into the shadow tree of new instances of this element.

The default value of this property is a template that includes an instance the standard element being wrapped, with a <slot> element inside that to pick up the element's light DOM content. For example, if you wrap an <a> element, then the default template will look like:

  :host {
    display: inline-block;
  <a id="inner">

The display styling applied to the host will be block for elements that are block elements by default, and inline-block (not inline) for other elements.

If you'd like the template to include other elements, then override this property and return a template of your own. The template should include an instance of the standard HTML element you are wrapping, and the ID of that element should be "inner".

Type: string|HTMLTemplateElement

Defined by WrappedStandardElement

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

value property

The text currently shown in the textarea.

Note that the text shown in the textarea can also be updated by changing the element's innerHTML/textContent. However, if the value property is explicitly set, that will override the innerHTML/textContent.

Type: string

wrap(extendsTag) static method

Creates a class that wraps a standard HTML element.

Note that the resulting class is a subclass of WrappedStandardElement, not the standard class being wrapped. E.g., if you call WrappedStandardElement.wrap('a'), you will get a class whose shadow tree will include an anchor element, but the class will not inherit from HTMLAnchorElement.


  • extendsTag: stringthe standard HTML element tag to extend

Defined by WrappedStandardElement