Text area that grows to accommodate its content
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.


Class hierarchy:

The element defines the following shadow parts:

  • inner: the inner standard HTML element
  • textarea: the inner standard HTML textarea

booleanAttributeValue(name, value) static method

Given a string value for a named boolean attribute, return true if the value is either: a) the empty string, or b) a case-insensitive match for the name.

This is native HTML behavior; see the MDN documentation on boolean attributes for the reasoning.

Given a null value, this return false. Given a boolean value, this return the value as is.


  • name: string
  • value: string|boolean|null

Defined by AttributeMarshallingMixin

contentSlot property

See contentSlot.

Defined by SlotContentMixin

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

extends property

The tag name of the standard HTML element extended by this class.

Defined by WrappedStandardElement

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

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

inner property

Returns a reference to the inner standard HTML element.

Type: HTMLElement

Defined by WrappedStandardElement

input event

Raised when the user changes the element's text content.

This is the standard input event; the component does not do any work to raise it. It is documented here to let people know it is available to detect when the user edits the content.

input event

Raised when the value property changes.

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

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

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.


  • 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.


  • changed: ChangedFlags

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: PlainObjectthe changes to apply to the element's state

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

Defined by ReactiveMixin

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.


  • 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

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

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 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