@polymer/lit-element

constructor

constructor(cssText: string);

property cssText

readonly cssText: string;

property styleSheet

readonly styleSheet: CSSStyleSheet;

property finalized

protected static finalized: boolean;

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

property render

static render: (
    result: TemplateResult,
    container: Element | DocumentFragment,
    options: any
) => void;

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

  Parameter Template

  to render.

  Parameter Node

  into which to render.

  Parameter Element

  name.

property renderRoot

protected renderRoot?: Element | DocumentFragment;

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

property styles

static readonly styles: CSSResult[];

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

method adoptStyles

protected 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](https://wicg.github.io/construct-stylesheets/#using-constructed-stylesheets).

method connectedCallback

connectedCallback: () => void;

method createRenderRoot

protected 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|DocumentFragment} Returns a node into which to render.

method initialize

protected 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.

method render

protected 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.

method update

protected update: (changedProperties: PropertyValues) => void;

• 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. *

  Parameter _changedProperties

  Map of changed properties with old values

constructor

constructor();

property finalized

protected static finalized: boolean;

• Marks class as having finished creating properties.

property hasUpdated

protected readonly hasUpdated: number;

property observedAttributes

static readonly observedAttributes: string[];

• Returns a list of attributes corresponding to the registered properties.

property properties

static properties: PropertyDeclarations;

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

property updateComplete

readonly 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(). This getter can be implemented to await additional state. For example, it is sometimes useful to await a rendered element before fulfilling this Promise. To do this, first await super.updateComplete then any subsequent state.

  Returns

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

method attributeChangedCallback

attributeChangedCallback: (name: string, old: string, value: string) => void;

• Synchronizes property values when attributes change.

method connectedCallback

connectedCallback: () => void;

method createProperty

static createProperty: (
    name: PropertyKey,
    options?: PropertyDeclaration
) => void;

• 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.

method disconnectedCallback

disconnectedCallback: () => void;

• Allows for super.disconnectedCallback() in extensions while reserving the possibility of making non-breaking feature additions when disconnecting at some point in the future.

method firstUpdated

protected firstUpdated: (_changedProperties: PropertyValues) => void;

• 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.

  *

  Parameter _changedProperties

  Map of changed properties with old values

method initialize

protected initialize: () => void;

• Performs element initialization. By default captures any pre-set values for registered properties.

method performUpdate

protected performUpdate: () => void | Promise<unknown>;

• Performs an element update.

  You can override this method to change the timing of updates. For instance, to schedule updates to occur just before the next frame:

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

method requestUpdate

requestUpdate: (name?: PropertyKey, oldValue?: any) => 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.

  Parameter name

  (optional) name of requesting property

  Parameter oldValue

  (optional) old value of requesting property

  Returns

  {Promise} A Promise that is resolved when the update completes.

method shouldUpdate

protected shouldUpdate: (_changedProperties: PropertyValues) => boolean;

• 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.

  *

  Parameter _changedProperties

  Map of changed properties with old values

method update

protected update: (_changedProperties: PropertyValues) => void;

• Updates the element. This method reflects property values to attributes. It can be overridden to render and keep updated element DOM. Setting properties inside this method will *not* trigger another update.

  *

  Parameter _changedProperties

  Map of changed properties with old values

method updated

protected updated: (_changedProperties: PropertyValues) => void;

• 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.

  *

  Parameter _changedProperties

  Map of changed properties with old values

method fromAttribute

fromAttribute: (value: string, type?: TypeHint) => Type;

• Function called to convert an attribute value to a property value.

method toAttribute

toAttribute: (value: Type, type?: TypeHint) => string | null;

• Function called to convert a property value to an attribute value.

call signature

(value: unknown, old: unknown): boolean;

property attribute

attribute?: boolean | string;

• Indicates how and whether the property becomes an observed attribute. If the value is false, the property is not added to observedAttributes. If true or absent, the lowercased property name is observed (e.g. fooBar becomes foobar). If a string, the string value is observed (e.g attribute: 'foo-bar').

property converter

converter?: AttributeConverter<Type, TypeHint>;

• Indicates how to convert the attribute to/from a property. If this value is a function, it is used to convert the attribute value a the property value. If it's an object, it can have keys for fromAttribute and toAttribute. If no toAttribute function is provided and reflect is set to true, the property value is set directly to the attribute. A default converter is used if none is provided; it supports Boolean, String, Number, Object, and Array. Note, when a property changes and the converter is used to update the attribute, the property is never updated again as a result of the attribute changing, and vice versa.

property noAccessor

noAccessor?: boolean;

• Indicates whether an accessor will be created for this property. By default, an accessor will be generated for this property that requests an update when set. If this flag is true, no accessor will be created, and it will be the user's responsibility to call this.requestUpdate(propertyName, oldValue) to request an update when the property changes.

property reflect

reflect?: boolean;

• Indicates if the property should reflect to an attribute. If true, when the property is set, the attribute is set using the attribute name determined according to the rules for the attribute property option and the value of the property converted using the rules from the converter property option.

property type

type?: TypeHint;

• Indicates the type of the property. This is used only as a hint for the converter to determine how to convert the attribute to/from a property.

method hasChanged

hasChanged: (value: Type, oldValue: Type) => boolean;

• A function that indicates if a property should be considered changed when it is set. The function should take the newValue and oldValue and return true if an update should be requested.

index signature

[key: string]: PropertyDeclaration;