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Class LitElement







renderRoot: Element | DocumentFragment

Node or ShadowRoot into which element DOM should be rendered. Defaults to an open shadowRoot.

Static Protected __computed

__computed: boolean = true

Marks class as having finished creating properties.

Static Protected finalized

finalized: boolean = true

Ensure this class is marked as finalized as an optimization ensuring it will not needlessly try to finalize.

Note this property name is a string to prevent breaking Closure JS Compiler optimizations. See updating-element.ts for more information.

Static properties

User-supplied object that maps property names to PropertyDeclaration objects containing options for configuring the property.

Static render

render: function = render

Render method used to render the lit-html TemplateResult to the element's DOM.


to render.


into which to render.




Type declaration

    • (result: TemplateResult, container: Element | DocumentFragment | ShadowRoot, options: ShadyRenderOptions): void
    • Parameters

      • result: TemplateResult
      • container: Element | DocumentFragment | ShadowRoot
      • options: ShadyRenderOptions

      Returns void

Static Optional styles

Array of styles to apply to the element. The styles should be defined using the css tag function.


Protected hasUpdated

  • get hasUpdated(): number


  • get updateComplete(): Promise<unknown>
  • Returns a Promise that resolves when the element has completed updating. The Promise value is a boolean that is true if the element completed the update without triggering another update. The Promise result is false if a property was set inside updated(). If the Promise is rejected, an exception was thrown during the update.

    To await additional asynchronous work, override the _getUpdateComplete method. For example, it is sometimes useful to await a rendered element before fulfilling this Promise. To do this, first await super._getUpdateComplete(), then any subsequent state.

    Returns Promise<unknown>

    The Promise returns a boolean that indicates if the update resolved without triggering another update.

Static observedAttributes

  • get observedAttributes(): string[]


Protected _getUpdateComplete

  • _getUpdateComplete(): Promise<unknown>
  • Override point for the updateComplete promise.

    It is not safe to override the updateComplete getter directly due to a limitation in TypeScript which means it is not possible to call a superclass getter (e.g. super.updateComplete.then(...)) when the target language is ES5 (https://github.com/microsoft/TypeScript/issues/338). This method should be overridden instead. For example:

    class MyElement extends LitElement { async getUpdateComplete() { await super.getUpdateComplete(); await this._myChild.updateComplete; } }

    Returns Promise<unknown>

Protected adoptStyles

  • adoptStyles(): void
  • Applies styling to the element shadowRoot using the static get styles property. Styling will apply using shadowRoot.adoptedStyleSheets where available and will fallback otherwise. When Shadow DOM is polyfilled, ShadyCSS scopes styles and adds them to the document. When Shadow DOM is available but adoptedStyleSheets is not, styles are appended to the end of the shadowRoot to mimic spec behavior.

    Returns void


  • attributeChangedCallback(name: string, old: string | null, value: string | null): void


  • connectedCallback(): void

Protected createRenderRoot

  • createRenderRoot(): Element | ShadowRoot
  • Returns the node into which the element should render and by default creates and returns an open shadowRoot. Implement to customize where the element's DOM is rendered. For example, to render into the element's childNodes, return this.

    Returns Element | ShadowRoot

    Returns a node into which to render.


  • disconnectedCallback(): void

Protected firstUpdated

  • Invoked when the element is first updated. Implement to perform one time work on the element after update.

    Setting properties inside this method will trigger the element to update again after this update cycle completes.


    • _changedProperties: PropertyValues

      Map of changed properties with old values

    Returns void

Protected initialize

  • initialize(): void
  • Performs element initialization. By default this calls createRenderRoot to create the element renderRoot node and captures any pre-set values for registered properties.

    Returns void

Protected performUpdate

  • performUpdate(): void | Promise<unknown>
  • Performs an element update. Note, if an exception is thrown during the update, firstUpdated and updated will not be called.

    You can override this method to change the timing of updates. If this method is overridden, super.performUpdate() must be called.

    For instance, to schedule updates to occur just before the next frame:

    protected async performUpdate(): Promise<unknown> {
      await new Promise((resolve) => requestAnimationFrame(() => resolve()));

    Returns void | Promise<unknown>

Protected render

  • render(): TemplateResult | void
  • Invoked on each update to perform rendering tasks. This method must return a lit-html TemplateResult. Setting properties inside this method will not trigger the element to update.

    Returns TemplateResult | void


  • requestUpdate(name?: PropertyKey, oldValue?: unknown): Promise<unknown>
  • Requests an update which is processed asynchronously. This should be called when an element should update based on some state not triggered by setting a property. In this case, pass no arguments. It should also be called when manually implementing a property setter. In this case, pass the property name and oldValue to ensure that any configured property options are honored. Returns the updateComplete Promise which is resolved when the update completes.


    • Optional name: PropertyKey

      (optional) name of requesting property

    • Optional oldValue: unknown

      (optional) old value of requesting property

    Returns Promise<unknown>

    A Promise that is resolved when the update completes.

Protected shouldUpdate

  • Controls whether or not update should be called when the element requests an update. By default, this method always returns true, but this can be customized to control when to update.


    • _changedProperties: PropertyValues

      Map of changed properties with old values

    Returns boolean

Protected update

  • Updates the element. This method reflects property values to attributes and calls render to render DOM via lit-html. Setting properties inside this method will not trigger another update.


    Returns void

Protected updated

  • Invoked whenever the element is updated. Implement to perform post-updating tasks via DOM APIs, for example, focusing an element.

    Setting properties inside this method will trigger the element to update again after this update cycle completes.


    • _changedProperties: PropertyValues

      Map of changed properties with old values

    Returns void

Static createProperty

  • Creates a property accessor on the element prototype if one does not exist. The property setter calls the property's hasChanged property option or uses a strict identity check to determine whether or not to request an update.



    Returns void

Static Protected finalize

  • finalize(): void

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